Pollution Of Air And Water - Class 8 Chemistry - Extra Questions

What is the percentage of nitrogen in air?

The percentage of nitrogen in air is 78.1 %


While __________ your teeth, leaving the __________ running may waste several ____________ of water. 

(Tap, liters, brushing, washing, drops)

While Brushing your teeth, leaving the tap running may waste several liters of water. 



What is the percentage of oxygen in air?

The percentage of oxygen in air is 20.9 %


Name two greenhouse gases.

Carbon dioxide and methane are two greenhouse gases.


Name the main components of air.

The main components of air are: 
1. Nitrogen $$(78 \%)$$
2. Oxygen $$(21 \%)$$
3. Carbon dioxide $$(0.04\%)$$
4. Argon $$(0.93\%)$$ 
5. Trace amounts of helium, neon, methane, hydrogen and water vapour.


Name the chemicals which are used in refrigerators and air conditioners and damage the ozone layer when released into the air.

CFCs contribute to ozone depletion in the upper atmosphere. A chlorofluorocarbon (CFC) is an organic compound that contains only carbon, chlorine, and fluorine, produced as a volatile derivative of methane, ethane, and propane. Many CFCs have been widely used as refrigerants, propellants (in aerosol applications), and solvents. 


$$CO_2$$ is the only atmospheric gas responsible for the greenhouse effect.
If true enter 1, else enter 0.

Several gases are responsible for the greenhouse effect other than $$CO_2$$. Methane, water vapour, ozone, and nitrous oxide also contribute to the greenhouse effect. It is estimated that $$CO_2$$ accounts for 76% of the total greenhouse gas emissions and, the remaining is due to other gases. 
Hence, the statement is false.


Instead of monitoring carbon dioxide, another gas that scientists could study to substantiate the fact that $$CO_2$$ concentration is steadily increasing in the atmosphere is $$O_2$$. Justify the statement.

In photosynthesis,

$$6CO_2 + 12H_2O \rightarrow C_6H_{12}O_6 + 6O_2 + 6H_2O$$

As that of atmospheric CO2 concentration increase that we observe is a product of temperature increase,  so based on the photosynthesis the O2 also increases in the atmosphere


Which one is a more effective greenhouse gas, $$CO_2$$ or $$H_2O$$?

 The average amount of water vapor in the atmosphere averaged for all locations is between 2 and 3%. Carbon dioxide levels are near 0.04%. That means there is more than 60 times as much water vapor in the atmosphere than carbon dioxide in average conditions. Both water vapor and Carbon dioxide are greenhouse gases. They both trap outgoing longwave radiation between the earth and the atmosphere. This has the effect of keeping temperatures warmer. Carbon dioxide is a more efficient greenhouse gas than water vapor when both are in equal quantities. However, they are not in equal quantities. There is much more water vapor than carbon dioxide in the atmosphere. In day-to-day weather forecasting, the greenhouse effect from water vapor is important while carbon dioxide is not.
So, $$H_2O$$ is a more effective greenhouse gas.




Smog is essentially caused by the presence of ________________ .

Smog is a mixture of smoke and fog. The smoke contains oxides of nitrogen that combine with fog and air pollutants to form smog.


List the gases which are responsible for greenhouse effect.

The gases which are responsible for the greenhouse effect are:
Carbon dioxide ($$\displaystyle CO_2 $$)
Methane ($$\displaystyle CH_4 $$)
Water vapor ($$\displaystyle H_2O $$)
Nitrous oxide ($$\displaystyle NO $$)
Ozone ($$\displaystyle O_3 $$)
Chlorofluorocarbons ($$\displaystyle CFCs $$)


Explain why sea water is not a potable water?

Seawater is entirely non-drinkable because of many reasons.

80% percent of seawater contains salt, which in turn is terrible for your health if you drink it. This is because when the water passes through your digestion system, there are little nutrients that can be extracted, and the small amount of water there is would be dried out. Second of all, the salt would make you thirstier, worsening your condition of thirst and probably motivating you to drink more. This can lead to death. Furthermore, dead fish, dissolved plastics, bird droppings, sand, bits of rock, and seaweed are inside seawater, and these, obviously, contain masses of bacteria that can make you very ill if taken in large amounts. So don’t drink seawater.



What are biodegradable and non-biodegradable detergents ? Give one example of each.

Biodegradable detergents can be degraded by bacteria. They have straight hydrocarbon chain. Example includes sodium lauryl sulphate.
Non-biodegradable detergents cannot be degraded by bacteria. They have highly branched hydrocarbon chains. Example includes $$sodium-4-(1,3,5,7-tetramethyloctyl)benzene \ sulphonate$$


You are a member of the municipal body of your town. Make a list of measures that would help your town to ensure the supply of clean water to all its residents.

To ensure the supply of clean water to all residents the following steps must be taken:
1. The main water source must be built in clean surroundings and should be maintained properly.
2. Chemical methods such as chlorination must be used for purifying water.
3. The area around water pipes must also be clean.


What are the different ways in which water gets contaminated?

Water gets contaminated by the following:
1. Discarding of untreated sewage into water bodies like lakes and rivers
2. Practice of bathing and washing near ponds, lakes or rivers
3. Practice of cremating dead bodies near river banks
4. Oil spills
5. Dumping of chemical and agricultural waste into water


Clear and transparent water is always fit for drinking. Comment.

Clear and transparent water is not always fit for drinking.

Even the clear, transparent water can contain harmful germs, spores, or microbes of many diseases that cannot be seen by the naked eyes so the clear water is not necessarily fit for drinking but boiled water is the safe solution to avoid diseases.


At an individual level, how can you help reduce air pollution?

Following steps can be taken to reduce air pollution at individual level:

1. Use of bicycles more than the fuel based vehicles.
2. Public transport can be used more than the private vehicles for commuting.
3. Planting of saplings will provide a pollution free air in near future.
4. Avoid burning leaves, trash, and other materials.
5. Avoid using gas-powered lawn and garden equipment


How would you confirm that a colourless liquid given to you is pure water?



Describe the threat to the beauty of the Taj Mahal.

Taj Mahal is our famous ancient monument which is showing signs of degradation, as its marble which is calcium carbonate, is being corroded by the frequent acidic rains. The reason for these acid rains is the presence of a refinery; the Mathura chemical refinery which is releasing acidic fumes like sulfur dioxide and nitrogen dioxide into the atmosphere.


Explain the circumstances leading to acid rain. How does acid rain affect us?

Acid rain is caused by burning of fossil fuels such as coal and petroleum products which releases a variety of pollutants such as sulphur and nitrogen oxides into the atmosphere. These pollutants react with water vapours present in the atmosphere to form sulphuric acid and nitric acid respectively. These acids come down with the rain, thereby resulting in acid rain.

Effects of acid rain:
1. Acid rain causes soil pollution by increasing acidity of soil, and damages crops.
2. It reacts with building materials like marble and corrodes them. Development of yellowish colour on the marble of the famous Taj Mahal is an effect of acid rain.


Write a note on global warming.

Continuous increase in temperature of the earth is called global warming.

Global warming is one of the greatest challenges that our planet is facing as we have been facing the continuous rise in the average temperature of the Earth’s climate system.

It occurs as a result of an increased release of greenhouse gases in the atmosphere. These gases, like carbon dioxide, methane, and water vapor in the atmosphere, trap solar radiations released back by the Earth.


Prepare slogans on greenhouse effect to announce in your school assembly.

Slogans:-
$$\longrightarrow$$ Solution to Global warming is reducing pollution and tree plantation.
$$\longrightarrow$$ Be Green to be free from Global warming.


What major harm is done to human beings by air pollution?

Air pollution is highly detrimental to human beings. Some of the harmful effects of air pollution on human beings are as follows:
(a) Polluted air increases the occurrence of respiratory disorders, especially in children.
Particular matter in polluted air may cause asthma, bronchitis, emphysema, etc.
(b) Carbon monoxide concentration is more in polluted air. Carbon monoxide when inhaled leads to headache, giddiness, reduced oxygen-carrying capacity of the blood, and sometimes death.
(c) Sulphur dioxide is poisonous. Even a small amount of sulfur dioxide causes respiratory diseases such as asthma, bronchitis, emphysema, etc. It causes irritation to the eyes, resulting in tears and redness.
(d) Hydrocarbons are carcinogenic. They cause cancer.


Classify the given sources of water pollution as natural and man made.
(i) Domestic waste
(ii) Dead animals
(iii) Oil spills
(iv) Ashes released due to forest fires.

  • Natural - dead animals and ashes released due to forest fires.
  • Man made - domestic waste and oil spills.


What is air? Name the major constituents of air. Also give their volume proportions in air.

Air is a mixture of gases. The major constituents of air are nitrogen, oxygen, carbon dioxide and argon. The percentage composition of constituents of air are as given below:
Name of Constituents% Composition
     Nitrogen gas  $$78.1$$%
     Oxygen gas  $$20.9$$%
     Carbon dioxide gas  $$0.03$$%
     Argon  $$0.9$$%
Other components of air are water vapour and dust particles.
1337688_634772_ans_646aee038d4f4a3f8cf905ff969b6abb.png


List down some methods to control air pollution.

The efforts required to be made by each individual to control pollution include:
(a) Switching to cleaner fuels like CNG.
(b) Using alternatives of fossil fuels like electricity and solar energy.
(c) Completely banning the burning of solid waste in open.
(d) Reduction of smoke emission and treatment of chimney smoke to remove solid carbon particles.


"Air is a mixture," Support this statement citing at least three evidences.

The following are the evidence that proves that air is a mixture-
    1. Air does not show the properties of its constituents.
    2. It does not have a fixed melting and boiling point.
    3. Air has a variable composition because the air at different places contains different amounts of various gases. It does not have a definite formula.


    The gas that is responsible for global warming is:

    Human activities contribute to the accumulation of $$CO_2$$  in the atmosphere. $$CO_2$$  traps heat and does not allow it to escape into space. As a result, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.
    So the answer is carbon dioxide.


    What is the role of chlorine in water purification?

    Chlorine is a highly efficient chemical liquid that destroys bacteria and is added to public water supplies to kill disease-causing pathogens, such as bacteria, viruses that commonly grow in water supply reservoirs and in storage tanks. It acts as a disinfectant.


    Define acid rain. What are its effects?

    Acid rain is caused due to presence of two strong acids in polluted air:  $$H_2SO_4$$ and $$HNO_3$$.
    Both $$SO_2$$ and $$NO_2$$ are released into the atmosphere by human activities. They react with oxygen and water in the atmosphere to form sulphuric acid and nitric acid respectively. These acids mix with rain or snow, i.e rainwater gets acidified on its way down to the earth. 

    Chemical reactions that occur in atmosphere are,

    $$2SO_2+O_2+2H_2O\rightarrow 2H_2SO_4$$

    $$4NO_2+O_2+2H_2O\rightarrow 4HNO_3$$

    Effects of acid rain:

    (i) $$Aquatic$$ $$life$$ - Acid rain causes lakes and rivers to become acidic and a drop in pH can destroy the ecological balance. Most aquatic animals cannot survive when the pH is less than 4. Certain species of algae and zooplankton are eliminated at pH less than 6. A reduction in the zooplankton and bottom fauna will affect the food availability for the fish population.

    (ii) $$Plants$$ - Acid rain decolorized leaf pigments i.e., chlorophyll is affected and agricultural productivity is decreased. Soil contains limestone and has natural buffering properties, but without this acidified soil means plant nutrients are leached from the soil. Aluminum is released damaging root systems, seeds stop germinating, helpful soil organisms are killed.
     
    (iii) $$Material$$ $$damage$$ - Metallic surfaces exposed to acid rain gets corroded. Building materials (limestone, marble, dolomite, mortar, and slate) are weakened on reaction with acid rain as water-soluble compounds are formed. Thus, acid rain is dangerous for historical monuments.






    What is greenhouse effect? Which atmospheric gases are responsible for this effect?

    The greenhouse effect received its name because the earth's atmosphere acts much like the glass or plastic roof and walls of a greenhouse. Sunlight enters a greenhouse through the transparent roof and heats the plants but the heat emitted by the plants in the form of infrared radiation cannot pass through the roof and walls. As a result, the temperature inside the house increases. An effect similar to the greenhouse is responsible for keeping the earth's surface warmer. The atmosphere around the earth acts like a glass of the greenhouse chamber. This is known as $$Greenhouse$$ $$effect$$.

    The gases present in the atmosphere which are responsible for the greenhouse effect are called $$greenhouse$$ $$gases$$. Example Carbon dioxide, water vapor, oxides of nitrogen, methane, etc


    Name five common water pollutants.

    Five common water pollutants are: 
    (i) Industrial discharge
    (ii) Detergents
    (iii) Toxic chemicals 
    (iv) Fertilizers 
    (v) Untreated sewage


    Suggest three ways to reduce greenhouse effect.

    Different ways to reduce greenhouse effects are -

    (i) Non-fossil energy sources should be adopted 
    (ii) The production and use of chlorofluorocarbons should be banned 
    (iii) Deforestation should be prevented 
    (iv) Population of the world must be stabilised.


    In the absence of greenhouse effect, what would be the mean temperature of the earth?

    Greenhouse gases in the air, mainly carbon dioxide, methane, and water vapor, trap radiation from the sun and act as a thermal blanket around the planet. Without the greenhouse effect, the average temperature of the earth could drop down to as low as $$-18^oC$$ and be covered in ice. Life, as we know, would not be able to survive.


    Describe the main effects of air pollution.

    Main effects of air pollution are:

    (i) $$Acid\space rain$$ refers to any precipitation which has pH less than 5.6.
    Acid rain results from the presence of two strong acids in polluted air: $$H_2SO_4$$ and to a lesser extent $$HNO_3$$. 

    (ii) $$Smog$$ is a combination of smoke and fog.
    Smog is of two type $$Classical\space smog$$ and $$Photochemical\space smog.$$

    (iii) $$Global\space warming$$ is a gradual increase in the overall temperature of the earth's atmosphere generally attributed to the greenhouse effect caused by increased levels of carbon dioxide, CFCs, and other pollutants.

    (iv) $$Ozone\space depletion$$ refers to the reduction of the concentration of ozone in the atmosphere. The ozone layer helps to protect life from harmful ultraviolet radiation. Ozone depletion occurs when chlorofluorocarbons (CFCs) and aerosol gases destroy the ozone molecules.


    What is acid rain?

    Acid rain is rain or any other form of precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions $$(low\ pH\ that\ is\ less\ than\ 5.6)$$.  Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acid rain.



    Which of the following gases qualify as greenhouse gases?
    $$CO,\ NO,\ NO_2,\ Cl_2, \ H_2,\ Ne$$.

    The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, nitrogen dioxide, and ozone. So greenhouses among the given are $$CO, NO$$ and $$NO_2$$.


    Answer the following questions.

    a) Write a short note on global warming.

    b) Name two common air pollutants.

    a) Global warming is that the long-term heating of Earth's climate system observed since the pre-industrial period (between 1850 and 1900) thanks to human activities, primarily fuel burning, which increases heat-trapping greenhouse emission levels in Earth's atmosphere.

    b) Two common air pollutants are particulate matter and oxides of sulphur and nitrogen.



    Write an essay on greenhouse effect.

    The 'greenhouse effect' is the warming of climate that results when the atmosphere traps heat radiating from Earth toward space. Certain gases in the atmosphere resemble glass in a greenhouse, allowing sunlight to pass into the 'greenhouse,' but blocking Earth's heat from escaping into space. The gases that contribute to the greenhouse effect include water vapor, carbon dioxide $$(CO_2)$$, methane, nitrous oxides, and chlorofluorocarbons (CFCs).

    On Earth, human activities are changing the natural greenhouse. Over the last century the burning of fossil fuels like coal and oil has increased the concentration of atmospheric $$CO_2$$. This happens because the coal or oil burning process combines carbon $$(C)$$ with oxygen $$(O_2)$$ in the air to make $$CO_2$$. To a lesser extent, the clearing of land for agriculture, industry, and other human activities have increased the concentrations of other greenhouse gases like methane $$(CH_4)$$, and further increased $$(CO_2)$$.

    The consequences of changing the natural atmospheric greenhouse are difficult to predict, but certain effects seem likely:

    • On average, Earth will become warmer. Some regions may welcome warmer temperatures, but others may not.

    • Warmer conditions will probably lead to more evaporation and precipitation overall, but individual regions will vary, some becoming wetter and others dryer.

    • A stronger greenhouse effect will probably warm the oceans and partially melt glaciers and other ice, increasing sea level. Ocean water also will expand if it warms, contributing to further sea level rise.

    • Meanwhile, some crops and other plants may respond favorably to increased atmospheric $$CO_2$$, growing more vigorously and using water more efficiently. At the same time, higher temperatures and shifting climate patterns may change the areas where crops grow best and affect the makeup of natural plant communities.



    Write a short note on global warming. Name some gases which cause greenhouse effect. What are the harmful consequences of this effect?

    The greenhouse effect received its name because the earth's atmosphere acts much like the glass or plastic roof and walls of a greenhouse. Sunlight enters a greenhouse through the transparent roof and heats the plants but the heat emitted by the plants in the form of infrared radiation cannot pass through roof and walls. As a result, the temperature inside the house increases. An effect similar to the greenhouse is responsible for keeping the earth's surface warmer. The atmosphere around the earth acts like a glass of the greenhouse chamber. This is known as greenhouse effect.

    Most of the heat radiated by the earth is absorbed by gases in the atmosphere and re-radiated back to the earth's surface. This increases the global temperature. This is known as global warming.

    The gases present in the atmosphere which are responsible for greenhouse effect and global warming are carbon dioxide, oxides of nitrogen, methane, ozone, chlorofluorocarbons, etc.

    Harmful consequences of the greenhouse effect are:
    i) Rise in sea level -  Higher sea level is caused when glaciers at the poles melt because of global warming. This would increase the frequency and severity of floods, damage coastal areas, i.e., low lying areas would submerge.

    ii) Changing patterns of rainfall - Patterns of rainfall would change worldwide causing large shifts in agriculturally productive areas.

    iii) Evaporation of water from aquatic systems: Global warming will cause more water to evaporate from aquatic systems and increase the concentration of water vapour in the atmosphere. The extra water vapour will amplify warming because water vapour itself is a greenhouse gas.


    Write a short note on global warming:
    Name two important sources of these pollutants.

    The greenhouse effect received its name because the earth's atmosphere acts much like the glass or plastic roof and walls of a greenhouse. Sunlight enters a greenhouse through the transparent roof and heat the plants but the heat emitted by the plants in the form of infrared radiation cannot pass through the roof and walls. As a result, the temperature inside the house increases. An effect similar to greenhouse is responsible for keeping the earth's surface warmer. The atmosphere around the earth acts like a glass of the greenhouse chamber. This is known as $$Greenhouse$$ $$effect$$.

    About half of the solar energy that enters the atmosphere is either reflected or absorbed by the molecules of the air.  UV radiations of shorter wavelengths are prevented from entering the troposphere by the presence of oxygen and the ozone layer in the stratosphere. The rays that do reach the surface of the earth are largely in the visible and infrared (heat) regions. These radiations are absorbed by the earth.
    Most of the radiation emitted by the earth lies in the infrared region.
    Almost 84% of the heat radiated by the earth is absorbed by gases in the atmosphere and re-radiated back to the earth's surface.
    Increase in the global temperature. This is known as $$Global$$ $$warming$$.

    The gases present in the atmosphere which is responsible for global warming are  Carbon dioxide, water vapour, oxides of nitrogen, methane, ozone, chlorofluorocarbons, etc

    Two important sources of pollutants are as follows:
    i) The common sources of CFCs are refrigerants, but fire suppression systems for aircraft and aerosols also emit CFCs into the atmosphere.

    ii) The common sources of $$CO_2$$ are burning of fossil fuels like coal, oil and natural gas in industries, power plants.
    Deforestation has caused an increase in the level of carbon dioxide.


    Give reasons for the following observations:
    (a) Air holes of a gas burner have to be adjusted when the vessels heated get blackened by the flame.
    (b) Use of synthetic detergents causes pollution of water.

    (a) Air holes of a gas burner have to be adjusted because the blackening of the vessel shows that the air holes of the gas stove are getting blocked and hence the fuel is not burning completely due to insufficient supply of oxygen.

    (b) Some of the detergents (synthetic) are not bio-degradable, which means they cannot be decomposed by microorganisms like bacteria and hence cause water pollution.


    Compare global warming phenomenon with ozone depletion phenomenon.

    Ozone depletion refers to the thinning and loss of ozone whereas global warming refers to the widespread warming of average temperatures across the globe caused primarily by the build-up of human-produced greenhouses gases, mostly carbon dioxide and methane, which trap heat in the lower levels of the atmosphere.

    The ozone layer allows some energy in and some energy out. The ozone protects us from UV rays, which can be very harmful. With less ozone, more UV- rays reach the earth's surface, harming humans and other animals as well as plants.



    What causes global warming?

    Global warming occurs when carbon dioxide and other air pollutants collect in the atmosphere and absorb sunlight that has bounced off the earth's surface. Normally this radiation would have escaped but these pollutants in the atmosphere trap the heat and cause the planet to get hotter leading to the increase in the global temperature and ultimately causing global warming.


    Name two gases that are mainly responsible for acid rain?

    Sulphur dioxide (SO2) and nitrogen dioxide (NO2) are the gases that react with water and oxygen and other gases to form acids like sulphuric and nitric, eventually resulting in acid rain.


    What is the major source of fresh water in the city/town/village? where can you live? Do you know of any activity which may be polluting this water source?

    Ground water is the major source of fresh water in my city, but from past few years due to anthropogenic activities it is getting polluted. Waste is being dumped on wastelands in my area due to his activity with time, when the waste gets decomosed. waste material is mixed within the soil and the harmful chemicals also get mixed. With time these chemicals move furthure in the ground and ultimately gets leached into the water table polluting ground water.


    Name any two sources which cause air pollution due to suspended particulate matter.

    Air pollution due to "suspended particulate matter" or SPM is caused
    through these sources-

    i. Industrial activities.

    ii.  Combustion of fuel by Automobiles.



    Give Reasons for the Following:
    Why air is considered as a mixture?

    The constituent particles of air are evenly distributed. This means mat a sample of air taken from any place would contain the constituent particles in the same proportion: composition. Air is constituted by more than one kind of substance and shows the properties of Its constituent particles. Therefore, air Is considered a mixture.



    Give reason for the following observation:
    Use of synthetic detergents causes pollution of water.

    Synthetic detergents are generally non-biodegradable, that is, they are not decomposed by microorganisms like bacteria. Hence, the use of synthetic detergents causes water pollution in lakes and rivers.


    The quality of air at various locations is monitored regularly by the government and other agencies? In what way can you use these data?

    We can be aware of and spread awareness of air pollution and its effect by using these data.


    We should plant trees and nurture the ones already present in the neighborhood. Why?

    There is a dire need for afforestation that is planting more trees. With time, pollution is increasing and so is global warming. In order to reduce global warming, we need more and more trees because trees use carbon dioxide to make food that is for photosynthesis, and give out oxygen. So when there will be more and more trees, there will be less effect of harmful gases like $$CO_2$$ on the environment. Plants prevent soil erosion. Plants maintain groundwater help. The more trees we plant, the more rain we get, thus, the more water for harvesting.


    The level of air pollution is higher at a busy traffic intersection. Why?

    At busy traffic intersection, many vehicles like cars, buses, scooters, and all other automobiles stop throughout the day. Each automobile releases a huge amount of toxic and pollutant gases. The suspended particle matter is suspended in the air around that area that makes it polluted.


    Carbon dioxide, thaneme, nitrous oxide and water vapour are known as heengrouse sesga.

    Carbon dioxide, methane, nitrous oxide and water vapour are known as greenhouse gases.


    Water which looks clean still has disease carrying ___________ and _____________ impurities. 
    (Insects, microorganisms, particles, dissolved, harmful)

    Water that looks clean still has disease-carrying microorganisms and dissolved impurities. 


    Many ___________ are responsible for causing _____________ pollution. Petroleum _____________ are a major source of ___________ pollutants like ______________ and ______________.
    (Sulphur dioxide, refineries, industries, nitrogen dioxide, gaseous, liquid,
    people, air).

    Many Industries are responsible for causing air pollution. Petroleum refineries are a major source of gaseous pollutants like sulphur dioxide and nitrogen dioxide.




    Water which is suitable for _____________ is called _______________ water. 

    (Washing, bathing, drinking, potable, soft).


    Water that is suitable for drinking is called potable water. 
    Potable water is described as water that is filtered and treated properly and is free from all the bacteria and harmful substances and is fit for drinking.


    Why is it advised that industries should switch over to cleaner fuels such as CNG and LPG in the Taj Mahal Zone in Agra?

    Less clean fuels like petrol and diesel are causing air pollution to this amount that it is resulting in acid which is harming the beauty of Taj Mahal as the white marble of the Taj is turning yellow because of the acids like sulphuric and nitric falling on it.


    Name any two water pollutants which are toxic for plants and animals.

    Pollutants like arsenic and lead are hazardous for both plants and animals. Arsenic leads to deformities by its accumulation in plant and animal bodies. Whereas lead causes morphological dysfunction.


    Whenever harmful substances such as wagese, toxic chemicals, silt, etc. get mixed with water, the water becomes potdulle.

    Whenever harmful substances such as sewage, toxic chemicals, silt, etc. get mixed with water, water becomes polluted.


    Vehicles produce high level of pollutants like carbon dioxide, nitrogen oxides, nobrac-moondexi and mosek.

    Vehicles produce high levels of pollutants like carbon dioxide, nitrogen oxides, Carbon-monoxide and smoke.


    Why can't we see air?

    We can't see air because it is colorless, odorless, and transparent gaseous matter. 


    How do you classify the various sources of water pollution?

    The various sources of water pollution are-

    Point source- Can be easily known.

    Non-point source- Cannot be easily known.



    How can we reduce, reuse, and recycle water?

    Water usage can be reduced in the following ways:

    • Close the tap while brushing teeth and open it only when necessary. 
    • Store the water from the leaking tap or fix leaking taps.
    • Don't waste water unnecessarily while bathing, washing clothes, washing dishes, etc.

    Water can be reused in the following ways:

    • Use the water filtered out by RO purifiers for washing floors. 
    • Use the water that you use for washing fruits and vegetables for watering plants.

    Water can be recycled in the following ways:

    • Purification of dirty water by filtration and various other methods.
    • Dirty water or sewage should be processed and purified before dumping into water bodies.



    Explain the traditional way of purifying water to make it fit for drinking.

    Earlier there was not much machinery, so there were not aqua guards or purifiers. But the water was still purified in a more convenient and reliable way, those methods are traditional methods. They are-

    Filtration:
    A type of filter or filter rods are used in this method. Candle type filter is a popular household filter.

    Boiling:
    Boiling raises the temperature of the water, therefore, killing all the germs and impurities in the water.

    Chlorination:
    Chlorine is added in water in the form of tablets or bleaching powder is added to the water.



    What is wind?

    Wind refers to the air movement from high pressure to low-pressure areas. It can be broadly divided into permanent, periodic, and local winds. 


    Fill in the blanks.
    Excessive burning of fossil fuels is a major cause of _______.

    Answer: Greenhouse effect

    Burning of fossil fuels results in the formation of greenhouse gases like carbon dioxide, that increase greenhouse effect. 


    How can you apply green chemistry for the following:
    To reduce the use of synthetic detergents.

    Synthetic detergents are non-biodegradable therefore their use in daily life is to be reduced. Good quality soaps to be prepared from vegetable oil. Soaps are biodegradable.


    During an educational trip, a student of botany saw a beautiful lake in a village. She collected many plants from that area. She noticed that villagers were washing clothes around the lake and at some places waste material from houses was destroying its beauty.
    After few years, she visited the same lake again. She was surprised to find that the lake was covered with algae, a stinking smell was coming out and its water had become unusable. Can you explain the reason for this condition of the lake?

    Domestic waste and organic compounds like detergents can provide nutrients to enhance the growth of algae and aquatic plants. These are decomposed by bacteria and give an unpleasant odor. This process is called eutrophication.


    Fill in the blanks:
    Air is a ___________ of gases.

    Air is a mixture of gases. It is combination of many gases, dust, and smoke which do not chemically combine to give new products. Individual components show individual properties and the components of air can be seperated easily by physical process.


    Fill in the blanks:
    Although we cannot see air, we can _________ it.

    Although we cannot see air, we can $$\text {feel}$$ it.


    What are the three methods of removing germs from natural water?

    Three methods to remove germs from water:
    1. Boiling 
    2. Filtration
    3. Chlorination



    Name two household methods to get safe drinking water.

    Methods to get safe drinking water: 
    1. By adding chlorine tablets. 
    2. By adding potassium permanganate crystals.



    Answer in brief: 

    What is the purpose of adding bleaching powder to water supplied to the town?

    Adding bleaching powder to water kills germs and harmful bacteria and viruses present in water and makes the water drinkable. 


    What is potable water?

    The water free from harmful chemical, which is transparent and odourless, safe for consumption by human beings is called potable water.


    State what do you understand by the term 'air'. Explain its importance to mankind.

    Air is a mixture of different gases like oxygen, nitrogen, helium, hydrogen, carbon dioxide, etc. It's major components are nitrogen and oxygen. Man cannot survive without air. The oxygen in air is essential for breathing. The carbon dioxide in air is taken by plants to produce food. Man's survival largely depends on plants, which in turn depend on air to survive.


    What are the main components of air? Write down the composition of three main gases present in the air.

    The main components of air are nitrogen, oxygen.
    The composition of three main gases present in the air are:
    Nitrogen $$78\%$$
    Oxygen $$21\%$$
    Carbon dioxide $$0.03-0.04\%$$
    Water vapour, dust particles, inert gases are in trace amounts.


    Name the following:

    A process that removes carbon dioxide from the air.

    A process that removes carbon dioxide from the air is called photosynthesis.


    State some important steps to avoid pollution of water.

    Steps to avoid pollution of water are :
    (a) Harmful wastes such as oils and chemicals should not enter the water. 
    (b) Proper toilets and sewage systems should be used to prevent human excreta, containing disease-causing organisms to enter into the water. 
    (c) Washing of clothes and bathing should be avoided near water sources.
    (d) Planting of trees near water sources including river banks also minimizes pollution. 
    (e) To minimize thermal pollution the water should be cooled before being discharged as a waste. 
    (f) Man should be made aware through various awareness programs and media about the harmful effects of water pollution and ways to control it.


    Suggest five measures to prevent air pollution .

    Five measures for the prevention of air pollution are:

    1. By using smokeless sources of energy , like solar energy and electrical energy , in place of conventional fossil fuels.
    2. By using filters for the smoke coming out of the chimneys of factories and power plants.
    3. By using internal combustion engines in vehicles for complete and efficient burning of fuel. 
    4. By locating industries away from residential areas.
    5. By growing more trees.


    What are the three main causes of water pollution?

    The main causes of water pollution are:
    1. Addition of waste products from homes to water bodies like lakes and ponds
    2. Addition of insecticides and pesticides from agriculture to the runoff water.
    3. Addition of toxic wastes from the industries to the rivers.


    How is greenhouse effect produced?

    The solar rays consist of heat radiations. These radiations can easily pass through the atmosphere. These radiations are absorbed by the Earth's surface and temperature of the Earth rises during the daytime. 

    At night, the Earth radiates out heat radiations which cannot easily penetrate through the atmosphere because carbon dioxide and clouds act as excellent reflectors. 

    Thus, heat radiations are trapped in the atmosphere which keeps the Earth warm during the night. This trapping of outgoing solar heat energy in Earth's atmosphere is the greenhouse effect.


    Why is distilled water not potable?

    Distilled water does not contain any salt or mineral required for our body. So it is not potable water.


    Name four ways by which pollution of air caused by humans is minimized.

    Pollution of air by humans can be minimized in the following manner:

    1. In the thermal power plants, steel plants, etc., smoke and ash should not be released into the air.
    2. Efficient internal combustion engines should be used in vehicles.
    3. Improved chulha or stoves should be used to minimize the production of smoke and carbon monoxide.
    4. We must grow more trees as they absorb harmful gases.


    Explain three methods of removing germs from natural water.

    Three methods to remove germs from water:

    1. Boiling: Boiling kills germs present in water. 

    2. Filtration: Using filters like candle filters remove impurities and germs from water.

    3. Chlorination: Adding chlorine tablets or bleaching powder to the water helps kill germs.


    Discuss harmful effects of greenhouse effect.

    A large amount of carbon dioxide in the polluted air results in an increase in the greenhouse effect which has raised the average temperature of the Earth by $$ 2^{\circ}\,C $$. This results in global warming which, in turn, will melt ice on the polar caps, thereby raising the levels of seawater by a few meters. This can result in submerging of coastal areas and islands causing excessive damage.


    Discuss two useful applications of greenhouse effect. 

    Two useful applications of the greenhouse effect are:

    1. Growing vegetables and flowers in snow-bound regions: Sheds using glass walls are built which allow smaller wavelength of solar heat radiations to pass into the shed but does not allow the longer wavelength of heat radiations to pass out during the night. This keeps the shed reasonably warm for flowers and vegetables to grow.

    2. Use of glass in keeping homes warm: In cold countries, the glass windows and doors allow the smaller wavelength of heat radiations of solar energy to pass into the rooms but do not allow a longer wavelength of heat radiations to pass out. Thus, the greenhouse effect takes place and rooms keep reasonably warm.


    Fill in the blanks:

    Oxygen is slightly ______ than air.

    Oxygen is slightly heavier than air. Molecular weight of oxygen is $$32$$ grams/ mole whereas molecular weight of air is around $$29$$ grams/mole.


    The major part of the air that does not support the burning of a candle is___

    The major part of the air that does not support the burning of candles is $$\text{nitrogen}$$.


    What steps should be taken to balance carbon dioxide in the atmosphere ?

    As global warming will cause an unbalanced ecological system, serious efforts should be made to balance the percentage of carbon dioxide in the atmosphere. Some of these steps are: 
    • Growing more trees and plants.
    • Using smokeless sources of energy like solar energy. biogas, etc.
    • Using filters in the chimneys of factories and powerhouses.


    What do you mean by green house effect?

    The greenhouse effect is a natural process that warms the Earth’s surface. When the Sun’s energy reaches the Earth’s atmosphere, some of it is reflected to outer space and the rest is absorbed and re-radiated by greenhouse gases. Greenhouse gases include water vapour, carbon dioxide, methane, nitrous oxide, ozone. The absorbed energy warms the atmosphere and the surface of the Earth allowing life on Earth to exist.


    Explain the term 'green house effect'.

    The sun’s rays warm the earth’s surface. A part of the radiation that falls on the earth is absorbed by it and a part is reflected back into space. The reflected radiation is trapped by greenhouse gases. The trapped radiations further warm the earth. The trapping of radiation by greenhouse gases is called the greenhouse effect.


    State the effects of green house gases on the atmosphere .

    Effects of the greenhouse effect on the atmosphere are as follows.
    • Greenhouse gases lead to an increase in temperature, which is called global warming.
    • An increase in temperature leads to the melting of glaciers, and polar ice caps are taking place which is leading to an increase in the sea level. This poses a threat of floods in the coastal areas.
    • Global warming increases the evaporation of water from water bodies which will increase water vapor in the atmosphere. An increase in water vapor further increases the temperature.
    • Global warming leads to change in rain patterns, which in turn results in a climatic shift and adversely affects plants and animals.
    • Greenhouses gases are responsible for ozone layer depletion.


    Excessive use of ___________  and ___________ by farmers cause water pollution.

    Excessive use of fertilisers and insecticides by farmers cause water pollution.


    How can we reduce global warming ?

    We can reduce global warming by taking the following measures:
    • Use of automobiles should be reduced by using public transport, bicycles and electric vehicles.
    • Trees should be planted and grown.
    • Burning of dry leaves and wood should be avoided.
    • Smoking should be avoided.
    • Educate people about the harmful effects caused by global warming.


    Explain the term 'global warming' . State two ways by which global warming can be reduced.

    Global warming is the increase in the temperature of the earth due to the increased concentration of greenhouse gases in the atmosphere.
    Ways by which global warming can be reduced-
    • The use of automobiles should be reduced by using public transport, bicycles and electric vehicles.
    • Trees should be planted and grown.
    • Burning of dry leaves and wood should be avoided.


    How do you propose to control :
    SOx emission

     Oxides of sulphur emission can be reduced,
    • By using coal or oil which has low sulphur content.
    • By using a scrubber, a device that absorbs gaseous pollutants.


    Why is it said that air is a homogeneous mixture of various gases?

    Air is a homogeneous mixture of gases as it is primarily made up of nitrogen, oxygen and other gases like carbon dioxide, argon etc. Its elements are not readily separated or distinguished from one another and have a uniform composition throughout the atmosphere.


    The substance that pollute the water are called _________.

    The substance that pollute the water are called $$\text{water pollutants}$$.


    What is acid rain? How does it effect us?

    Nitrogen, sulphur and carbon dioxide form sulphuric acid, nitric acid, nitrous acid, sulphurous acid, carbonic acid, etc. by reacting with water. They convert rain into acid rain and fall on earth. Due to acid rain, monuments like Taj Mahal are deteriorating. This is called marble cancer. It also deteriorates buildings, monuments, bridges sculptors, railing and railway lines. Ponds and soil become acidic. It affects the absorption of minerals by the plants from soil and it becomes infertile. It causes burning in eyes and skin. It damaged membranes of plants and animals.

    Measures Taken By Supreme Court To Conserve Historical heritage:
    1. Order is given to industries to use CNG and LPG fuels near the Taj Mahal area.
    2. Order is given to use lead-free petrol by vehicles in area Taj Mahal.


    Write the methods to prevent air pollution.

    Steps for air pollution Control:
    1. Chimneys of all industries should have Gas absorbers.
    2. Pollutant particles should be removed through filters.
    3. Time-to-time combustion engine should be checked.
    4. Ideal fuels should be used, so less smoke and harmful gases would emit.
    5. Waste gases and smoke should be oxidized so there would be less pollution.
    6. Industries should be established away from the city.
    7. Deforestation should be banned.
    8. More and more plantations should be done.
    9. Public awareness programs should be conducted, for environmental cleanliness.
    10. To drive automobiles leadless petrol, CNG and LPG should be used.
    11. Crackers should be banned on Diwali to decrease pollution.
    12. Government should carry out monitoring air quality regularly.
    13. Wind energy, solar energy, and hydropower should be used as alternative sources of energy.
    14. Lakh of plants should be planted in the month of July under forest or van Mahotsav.
    15. The use of Vehicles should be less and the use of bicycles should be encouraged.
    16. By putting garbage into the compost pit.


    Match List-I with List-II

    • Due to acid rain, the marble of the Taj Mahal has become yellow and is degrading. This is known as 'Marble cancer'.
    • Taj Mahal is a historical heritage and is one of the seven wonders of the world.
    • Ganga river project was launched by the government to Save Ganga river.
    • Van Mahotsav is celebrated in the first week of July and lakhs of trees are planted.
    Therefore correct answers are:
    A) Marble cancer $$ \rightarrow $$ Marble degradation(3)
    B) Taj Mahal  $$ \rightarrow $$ Historical heritage(1)
    C) Save Ganga $$ \rightarrow $$  Ganga river project(4)
    D) Van Mahotsav $$ \rightarrow $$ Plantation tree(2)



    Write in detail about the danger over river Ganga.

          Ganga is one of the holy rivers among the famous rivers of India. It is also called Gangamata. Ganga water remains pure (potable) if kept for many days. It nourishes the population of North and East India. According to the study of WWF (World Wild Life Federation ), the Ganga is one out of the ten rivers of the world whose existence is in danger. Those cities which are located on the banks of the river Ganga dump garbage, treated waste, dead bodies, flowers, pooja material, polythene directly in this river. Hence it is polluting day by day. 

            In 1985 to save this river, Ganga River Plan was started but increasing population and industrialization have already harmed this river. At present Government has started an integrated plan 'Namami Ganga' for its conservation. But to make it successful participation of all Government departments and people is a must.


    Clean drinking water is called ___________.

    Clean drinking water is called potable water.


    The average temperature of the atmosphere is continuously increasing, this effect is called _________.

    The average temperature of the atmosphere is continuously increasing, which is called $$\text{global warming}$$.


    What is potable water?

    Water that is fit for drinking is termed as potable water.


    How water can be purified?

    Water can be purified by boiling. Boiling is the simplest method to purify water. Apart from this there are other methods like filtration, distillation, by using water purifier etc.


    The number of vehicles as well as use of petrol, diesel and kerosene are rising day by day. The smoke from the vehicles mixes with the air and causes air pollution. Write your suggestions and views for reducing air pollution.

    Here are a few things we can adopt to reduce air pollution due to rising number of vehicles: 
    1. Switch off the engine at traffic lights or at a place where you have to wait. 
    2. Ensure correct pressure in tyres. 
    3. Ensure regular maintenance of the vehicle. 
    4. Sustainable use of petroleum products is a must so that future generations can also use them. 
    5. Use of unleaded petrol, CNG, LPG to minimise pollution. 


    Why is it necessary to purify the water? Explain the different methods for purifying water.

    Sources of water like rivers and lakes contain many chemicals, pathogens, and other pollutants. Therefore, it is necessary that the water supplied to homes is purified before being made available for human use. The water supply network of the municipal authorities follows the following methods for the purification of water.
    Water purification at Municipality:
    (a) Sedimentation
    (b) Filtration
    (c) Disinfection
    The water supplied to homes can now be used for domestic purposes but may still not be fit for drinking. Water that is safe for human consumption is called potable water. Potable water is free from pollutants, impurities, and pathogens. It is clean, clear, transparent, odorless, and pleasant in taste with the desired quantity of oxygen and salts dissolved. Since there is no simple way to determine the purity of water further before drinking. Some methods used for domestic and industrial purification of water are:
    (a) Boiling
    (b) Distillation



    How does detergent cause water pollution?

    Detergents are non-biodegradable and cause water pollution.
    They inhibit the oxidation of organic substances present in wastewater because they form a sort of envelope around them.
    They form stable foam in rivers that extend over several hundred meters of the river water.


    Which phenomena causes global warming?

    Greenhouse effect is the phenomena that causes global warming.


    Name two gases which are responsible for green house effect.

    Carbon dioxide and methane.


    What is Green House Effect? How it affects life?

    It may be defined as "the progressive warming up of the Earth's surface due to blanketing effect of man-made carbon dioxide in the atmosphere". It is the phenomenon due to which the Earth retains heat. The major gases responsible for greenhouse effect, are carbon dioxide ($${CO}_{2}$$) methane $$({CH}_{4})$$, nitrous oxide $$({N}_{2}O)$$ and chlorofluorocarbons (CFCs). Among these, $${CO}_{2}$$ is the most common gas which causes this effect.
    Consequences of Green House Effect:
    Its effect is detrimental to the environment. These are given as below:
    Due to the greenhouse effect, the temperature of the Earth increases.
    This may lead to the melting of glaciers and polar ice caps.
    The level of the sea may rise which causes floods.
    It affects the production of food crops.
    The fertile land may become barren and aquatic life will be seriously affected.


    Discuss the consequences of global warming in the following.
    (a) In ocean islands

    The ocean islands will be submerged. The ocean absorbs most of the excess heat from greenhouse gas emissions, leading to rising ocean temperatures. Increasing ocean temperatures affect marine species and ecosystems. Rising temperatures cause coral bleaching and the loss of breeding grounds for marine fishes and mammals.


    What are the sources of water pollution? What steps could be taken to prevent water pollution?

    Sources of water pollution:
    There are the following sources of water pollution:
    1. Natural sources:
    Pathogens which include bacterial and other organisms
    Faeces of organisms
    Remains of plants and animals
    Minerals from mines etc
    2. Man made sources:
    Domestic sewage like rotten, fruits, soaps, detergents etc
    Municipal sewage released from houses, public toilets, bathing etc
    Industrial wastes
    Industrial effluents
    Agricultural discharge like fertilizers, pesticides etc.
    Prevention of water pollution:
    The following steps could be taken to prevent water pollution:
    Prohibition in bathing and washing of clothes in rivers and streams and also in discharging untreated or treated sewage in water bodies.
    Judicious use of pesticides and fertilizers
    Re-use of water after treatment of waste water for irrigation and municipal purposes
    Regular monitoring of water bodies
    Use of waste water treatment plant in industries hospitals etc


    What measures should be taken to reduce acid rains?

    Measures which should be taken to reduce acid rains:
    $$\bullet$$ Reduce the excessive use of fossil fuels.
    $$\bullet$$ Before using fossil fuels, remove sulfur compounds from them as far as possible.


    What do you mean by greenhouse effect?

    The greenhouse effect is a process by which solar radiation is absorbed by greenhouse gases and the temperature of Earth's atmosphere is increased. This increase in the temperature of the surroundings is responsible for global warming. Gases like Carbon dioxide, methane, nitrous oxide, water vapour, etc., trap heat radiation and are called greenhouse gases



    Which gases are responsible for the greenhouse effect?

    The gases responsible for greenhouse effect are carbon dioxide, methane, nitrous oxide, chlorofluorocarbons and water vapour.


    Write two remedies to prevent water pollution.

    Two remedies to prevent water pollution are:
    1. Stop dumping of waste in water resources.
    2. Reduce the use of fertilizes and pesticides.


    What are the pollutants attacking the Taj Mahal? How are they being produced in the atmosphere?


    1933969_1877398_ans_8bd86211de2c4ef286c8a6c8c260db10.jpg


    How synthetic detergents present as water pollutants create problems?

    Synthetic detergents are generally non-biodegradable. They are not easily decomposed by bacteria present in water bodies as a result these detergent materials remain there for a long period and cause water pollution. This also affect the aquatic animals, plants present in water bodies.


    What is the Greenhouse effect? How does it affect the global climate?

    Greenhouse effect is the phenomenon in which the earth's atmosphere traps the heat from the sun and prevents it from escaping into outer space. Gases like $$CO_2$$, methane, ozone, CFC are called greenhouse gases.
    The heat from the sun after being absorbed by the earth is absorbed by the greenhouse gases and then radiated back to the earth. So the environment of the earth becomes warm. Due to the increased greenhouse effect, the global climate became warmer and it is termed global warming.


    Why is acid rain considered as a threat to the Taj Mahal?

    The Taj Mahal is made up of marble. The acid rain contains $$H_2SO_4$$ which attacks the marble $$(CaCO_3)$$ thereby pitting it, discoloring it, and making it lusterless.

    $$CaCO_3+H_2SO_4 \longrightarrow CaSO_4+CO_2+H_2O$$


    How is the pollution of river water caused? Which plans have been made by the Government of India to stop this pollution?

    Rive water pollution is caused by,
    1. Large amounts of domestic, municipal, and agricultural wastes are disposed of in the rivers.
    2. Huge quantities of untreated sewage and industrial effluents are disposed of in rivers. These reduce the quality of water and also the self-cleansing capacity of the rivers.
    3. Dumping of used oil and paints into river water has also polluted the river.
    4. Pathogens are water pollutants, these are the disease-causing agents that enter the water from domestic sewage and Animal Excreta.

    Plans made by the Government of India to stop the water pollution are,
    1. Preparation of action plan for sewage management and restoration of water quality in aquatic resources by state governments.
    2. Setting up of monitoring network for assessment of water quality.
    3. Ganga Action plan for protecting river Ganga from furthermore pollution.


    What do you understand by the greenhouse effect? What are the major greenhouse gases?

    The warming of the earth due to re-emission of sun’s energy absorbed by the earth followed by its absorption by $$CO_2$$ molecules and $$H_2O$$ vapour present near the earth's surface and then its radiation back to the earth is called the greenhouse effect.

    Though $$CO_2$$ is the main gas in the greenhouse effect, there are some other greenhouses gases also like methane, chlorofluorocarbons, ozone, nitrous oxide, and water vapour.


    Combustion of fossil fuels generates a lot of air pollution. Can you suggest any two alternative sources of energy which do not cause any pollution?

    The combustion of fossil fuels generates a lot of air pollution. The burning of these fuels releases harmful gases. To reduce this effect, we can use alternate sources to generate energy such as:
    1) Solar energy 
    2) Wind energy 
    3) Hydroelectricity 


    Name four effects of air pollution.

    Four effects of air pollution are-
    (I)  It causes acid rain.
    (ii) It damages crops and trees.
    (iii) It degrades the soil quality. 
    (iv) It causes respiratory disorders.


    What is global warming? How does greenhouse effect cause global warming?


    1874634_831987_ans_15178ab35c404a86b05f5b4ffe2b6d5e.jpg


    Describe the threat to the beauty of the Taj Mahal.

    Acid rain is a major threat to the beauty of the Taj Mahal. When acid rains fall on the monument (which is completely made of marble), they react with marble to form a powder-like substance that is then washed away by the rain. This phenomenon is known as marble cancer. Also, the soot particles emitted from the Mathura oil refinery located near Agra are leading to the yellowing of the marble.


    Name three greenhouse gases.

    $$\text{Carbon Dioxide, Methane, Nitrous Oxide}$$ etc.


    What do CFCs stand for? Name some devices where CFCs are used. Why CFCs are considered as pollutants?

    CFCs stands for Chlorofluorocarbons

    Chlorofluorocarbons are the gases used in electric appliances like air conditioners and refrigerators. CFCs are made up of "Chlorine, Fluorine, and Carbon" elements. CFCs are considered pollutants as they contribute to the depletion of the ozone layer.



    A lot of dry leaves are collected in a school garden and are burnt every day. Do you think that it is right to do so? If not, what should be done to dispose off the dry leaves?

    Burning dry leaves causes air pollution because various harmful gases are released like carbon monoxide. Therefore, instead of burning, they should be composted as it does not give rise to any type of pollution, in fact, act as manure for the plants and trees.


    It is said, "$$CO_2$$ contributes to global warming." Explain.

    Carbon dioxide is a harmful gas that contributes to air pollution and global warming. It is consumed by plants and trees for photosynthesis, so the amount of carbon dioxide is reduced in the atmosphere, and in return they give oxygen. 

    But with time, industrialization is happening at a high speed and trees are being cut at an enormous rate. So the level of carbon dioxide is increasing in the atmosphere. As a result, the sun's heat is increasingly being trapped on earth's surface. This is increasing earth's temperature at an alarming rate, and thus causing global warming.


    Write the fullform of CFC. What are their uses? Why are CFCs considered pollutants?

    CFC stands for chlorofluorocarbons. They are used in refrigerators, air conditioners and aerosol sprays. They are considered pollutants as they damage the ozone layer which protects us from the harmful UV rays of the sun. Because of the damage to the ozone layer, harmful UV rays can reach the earth surface and cause harm to the living organism.


    Match the activity given in Column I with the type of pollution created by it given in Column II.

    Column I (Activity )Column II (Effect)
    (i) Releasing gases to the atmosphere 
    after burning waste material containing sulphur.    		$$SO_2$$ causes acid rain, water pollution, formation of smog, breathing problems, damage to buildings, corrosion of metals.
    (ii) Using carbamates as pesticidesCarbamates are pesticides which are more biodegradable but severe nerve toxins hence more harmful to humans.
    (iii)Using synthetic detergents for washing clothes.Synthetic detergents are non-biodegradable and cause water pollution.
    (iv) Releasing gases produced by automobiles and factories in the atmosphere.Gases released from automobiles and factories in atmosphere cause photochemical smog, damage to plant life, inducing breathing problems and water pollution.
    (v) Using chlorofluorocarbon compounds for cleaning computer partsPresence of Chlorofluorocarbons in atmosphere are responsible for damaging ozone layer.


    Who are the people who usually suffer from ‘black lung disease’ and who are those who suffer from ‘white lung disease’?

    Coal miners suffer from black lung disease and textile workers suffer from white lung disease.


    What is the Greenhouse effect? Why is it so-called? What are its consequences?

    • The greenhouse effect is a natural process that warms the Earth’s surface. When the Sun’s energy reaches the Earth’s atmosphere, some of it is reflected back to space and the rest is absorbed and re-radiated by greenhouse gases.
    • Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, ozone, and some artificial chemicals such as chlorofluorocarbons (CFCs).
    • The absorbed energy warms the atmosphere and the surface of the Earth. This process maintains the Earth’s temperature at around 33 degrees Celsius warmer than it would otherwise be, allowing life on Earth to exist.
    The process is called the greenhouse effect because the exchange of incoming and outgoing radiation that warms the planet works in a similar way to a greenhouse.
    • The main effects of increased greenhouse gases are:
    • Global Warming
    It is the phenomenon of a gradual increase in the average temperature of the Earth’s atmosphere. The main cause for this environmental issue is the increased volumes of greenhouse gases such as carbon dioxide and methane released by the burning of fossil fuels, emissions from vehicles, industries, and other human activities.
    • Depletion of  Ozone Layer
    The ozone layer protects the earth from harmful ultraviolet rays from the sun. It is found in the upper regions of the stratosphere. The depletion of the ozone layer results in the entry of harmful UV rays to the earth’s surface that might lead to skin cancer and can also change the climate drastically.
    The major cause of this phenomenon is the accumulation of natural greenhouse gases including chlorofluorocarbons, carbon dioxide, methane, etc.
    • Smog and Air Pollution
    Smog is formed by the combination of smoke and fog. It can be caused both by natural means and man-made activities.
    In general, smog is generally formed by the accumulation of more greenhouse gases including nitrogen and sulfur oxides. The major contributors to the formation of smog are automobile and industrial emissions, agricultural fires, natural forest fires, and the reaction of these chemicals among themselves.



    How is greenhouse effect caused? Give names of the greenhouse gases.

    A part of the solar radiation which falls on the earth's surface is absorbed by the earth's surface and the other part is reflected into the atmosphere. These reflected radiations are trapped by atmospheric gases. As a result, there will be an increase in the earth's temperature. Especially it is trapped by greenhouse gases. This phenomenon is known as the greenhouse effect. The greenhouse effect is mainly caused due to carbon dioxide ($$CO_2$$) gas. Some other greenhouse gases are Methane, nitrous oxides, and water vapor. 


    List at least five important sources responsible for water pollution.

    Five important sources responsible for water pollution are:
    (I) Because of land disturbance by the construction of houses, industries, roads, etc.
    (ii) chemical pollution from industries, mines. 
    (iii) Inadequate sewage collection and treatment. 
    (iv) Increase in fertilizers to grow more food.
    (v) Litter, which causes diseases and has a negative visual impact.


    How does the excessive use of fossil fuels cause global warming?

    The greenhouse gases(like carbon dioxide) given out by the burning of fossil fuels increase the temperature of the atmosphere and cause global warming.


    How can 'greenhouse effect' be both beneficial and harmful for life on earth?

    Greenhouse is beneficial because this principle is applied to grow plants in colder regions. 
    Carbon dioxide increases the temperature of atmosphere. Due to rise in temperature, ice in the polar regions may melt, causing floods. So it is harmful for life on earth.


    Class 8 Chemistry Extra Questions