CBSE Questions for Class 11 Medical Chemistry Environmental Chemistry Quiz 3 - MCQExams.com

• Stratosphere is the region of atmosphere where ozone layer is present, hence ozone depletion occurs in stratosphere.
  
• Biosphere is the region of surface and atmosphere of earth occupied by living organisms, hence unrelated to the question.
• Atmosphere is a broad term which becomes irrelevant when already a specific option ie stratosphere, is given in the choices.
• Microsphere is a small particle which has a different environment than its surroundings, hence incorrect.

A. Correct Option: D

B. Explanation for the correct option:

• Phosphate pollution is directly linked with the production of untreated sewage wastes and agricultural fertilizers into the water body.
•  An agricultural fertilizer such as phosphate is an important compound of fertilizers used in the crop fields which is further passed down to the water bodies.
•  Phosphate stimulates algae growth and causes algal bloom and affects the water quality which is very unsafe to the different species living in the water bodies.  

$$\textbf{Correct answer: D}$$  

$$\textbf{Solution:}$$  

$$\textbf{Option (A):}$$  

$$\bullet$$ The 2,4-Dichlorophenoxyacetic acid is a type of 'organochlorine'. These are hydrophobic and lipophilic molecules. 

$$\textbf{Option (B):}$$  

$$\bullet$$ DDT or Dichloro-diphenyltrichloroethane is also lipophilic in character as it belongs to the ‘organochlorine' type. 

$$\textbf{Option (C):}$$  

$$\bullet$$ BHC or Benzene hexachloride is lipophilic in nature with its organochlorine character.

$$\textbf{Option (D):}$$  

$$\bullet$$ Since all these pesticides are lipophilic in nature, they can easily accumulate in the fatty tissues of animals.

$$\bullet$$ As these compounds accumulate in the body of the herbivores and from there remain in the ecological pyramid, and result in biomagnification. 

$$\bullet$$ This is why all such lipophilic pesticides are banned in western countries. This is because such pesticides are not safe.

Hence, the correct answer is option (D).

• Ozone molecule ( $$O_3$$ ) is formed by the interaction of 3 oxygen molecules.
• Ozone is highly reactive and can react with air and create nitrogen dioxide, another air pollutant which are poisonous for humans.
• It is also present in the stratosphere as a layer and protects living organisms by keeping UV rays from reaching the earth's surface.
  

Explanation:

• The compounds, which are responsible for the depletion of ozone layer are $$CFCl_3$$ , $$NO$$ and $$Cl_2$$ .
• Option A), $$CH_4$$ do not causes depletion of ozone layer.

• Option B),  $$ClF_3\ +\ UV \space radiations → Cl∙\ +\ ∙CFCl_2$$

  $$Cl∙ + O_3 → O_2 + ClO∙$$
  

 Solution

Correct answer is option C.

Explanation for correct option:

• The ozone layer, also called the stratosphere, is composed of the ozone gas (90% of the total ozone in the atmosphere).
• The main cause of ozone depletion and the ozone hole is manufactured chemicals, especially manufactured halocarbon refrigerants, solvents, propellants, and foam- blowing agents (chlorofluorocarbons (CFCs), HCFCs, halons).

Correct Answer: Option A

Explanation:

The ozone layer is present in the stratosphere region of the earth which is present approximately $$15 - 30$$ km above the surface of the earth.

It contains higher concentrations of ozone in comparison to other layers.