CBSE Questions for Class 11 Medical Chemistry Environmental Chemistry Quiz 2 - MCQExams.com

The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It starts at 10–13 km (33,000–43,000 ft; 6.2–8.1 mi) and ends at 50 km (160,000 ft; 31 mi).

Afforestation is the process of planting trees, or sowing seeds, in a barren land devoid of any trees to create a forest. The benefits of this practice, which is called agroforestry, are:

1. It provides a supply of timber, fruit, and fodder for cattle apart from crop production
2. It prevents soil erosion and thus conserves soil.
3. It enables better retention of water
4. It shields crops from excessive wind and sun damage

In terms of the environmental benefits, planting trees is always beneficial whether it takes place in a barren land or is used as a method to regenerate a depleted forest. Trees help check atmospheric carbon dioxide; large scale afforestation can curb the problems caused due to burning of fossil fuels, industrialization and so forth.

Humus refers to the fraction of soil organic matter that is amorphous and without the cellular cake structure characteristic of plants, micro-organisms or animals. Humus has a characteristic black or dark brown color and is organic due to an accumulation of organic carbon found in Horizon - A. The three major horizons are: (A) surface horizon, (B) subsoil and (C) substratum. Some soils have an organic horizon (O) on the surface. Hard bedrock, which is not soil, uses the letter R.

• 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. The greenhouse gasses trap heat and make air less permeable, thus, raising the temperature across the globe which is responsible for the melting of polar ice caps.

• Acid rain is rain or any other form of precipitation that is unusually acidic, i.e. it has elevated levels of hydrogen ions. It can have harmful effects on plants, aquatic animals, and infrastructure. Acid rain damages buildings and structures because it dissolves the stone or corrodes the metal that is exposed to the weather. The phenomenon is also called Marble cancer.

• The ozone layer or ozone shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet radiation. Ozone layer depletion increases the amount of ultraviolet-B (UVB) rays that reach the Earth's surface. Negative effects include skin cancers, eye cataracts, and immune deficiency disorders in human beings. It also affects plant growth, reducing agricultural productivity. 

• Photochemical smog is the chemical reaction of sunlight, nitrogen oxides, and volatile organic compounds in the atmosphere, which leaves airborne particles and ground-level ozone. In photochemical smog, nitrogen oxides are irritating to the eyes, skin, nose, mucous membranes, and respiratory tract.

Hence, the correct matches will be:

$$A-3, B-2, C-1, D-4$$

Therefore, option (B) is the correct answer. 

1. Population explosion ends up in over use of natural resources and hence pollutes the environment. For example higher population pollutes our water resources around us.
2. industralisation ends up in the release of effluents into water bodies or spoiling land areas.
3. Cutting down trees for fuel and burning end up in air pollution.
4. Urbanisation after deforestation ends up in polluted atmosphere and deficit of fresh water for human use.