Answer: Option B. -> Mountains  
:
B and C
Soil erosion can be easily prevented by afforestation. But it is very difficult to practice afforestation on mountains and hilly regions. The uneven terrain and steep slopes in these regions facilitate soil erosion. Areas with bare vegetation will not have the soil tightly held by the roots of plants. Hence, restoring soil erosion will be difficult in these areas.
 

Answer: Option C. -> CFC
:
C
Chlorofluorocarbon (CFC) is an organic compound that contains only carbon, chlorine, and fluorine. This compound does not get degraded by any biological process. CFC reacts with ozone layer and it results in the depletion of ozone layer.

Answer: Option C. -> Usage of fertilisers in farmlands.
:
A, B, C, and D
Water pollution occurs when pollutants are directly or indirectly discharged into water bodies without adequate treatment to remove harmful compounds. 
Major causes of water pollution are:
1. Wastes from industries and sewage getting dumped into fresh water bodies.  
2. Use of fertilisers and pesticides in farmlands.
3. Releasing water from dams into rivers which causes a variation of water temperature in rivers.
 

Answer: Option A. -> Carbon dioxide is a greenhouse gas.
:
A and B
The greenhouse gases do not let the radiations from the sun entering our atmosphere escape from the Earth. Thus it enhances the average surface temperature of the Earth which leads to global warming, i.e., an increase in the ambient temperature of the Earth causing several disasters.
The greenhouse gases responsible for greenhouse effect are:
- Water vapour
- Carbon dioxide
- Methane
- Ozone

Answer: Option A. -> Use of pesticides, insecticides and other chemicals in farmlands.
:
A, B, and C
The addition of harmful or toxic chemicals to the soil which renders it unproductive is called soil pollution. 
Causes:
1. The use of synthetic toxic chemicals such as pesticides, insecticides, fertilizers, which are used on plants, alters the nature of the soil and gradually decrease its productivity.
2. Industrial activities generate different kinds of wastes. Some of them are highly toxic in nature. The by-products are contaminated and are emitted into the land bodies nearby.
3. Waste materials are disposed of by the means of the landfill, which harmfully affects the fertility of the soil.
4. Acid rain, which is caused by air pollution, deposits acids in the soil through water runoffs. The acids are particularly harmful to the soil.

Answer: Option A. -> Heart diseases
:
A, B, and D

• Unburnt carbon particles, oxides of nitrogen and sulphur, smog, etc., are the different pollutants that are present in the atmosphere. Studies have shown that regularly breathing air that contains any of these substances increases the incidence of allergies, cancer and heart diseases.


• Cholera is a water-borne disease caused due to contaminated water bodies.

Answer: Option D. -> Nitrification
:
D
Nitrification is the biological oxidation of ammonia to nitrite followed by oxidation of nitrite to nitrate, performed by nitrogen fixing bacteria. It is a vital step in the nitrogen cycle and is essential for the survival of plant life.

Answer: Option A. -> Ozone hole is aggravated due to modernisation and use of technology without environment sustainability.
:
A and C

Ozone hole region in Antarctica is due to thinning of the stratospheric ozone layer. Ozone hole is caused by increasing concentrations of ozone-depleting chemicals in the stratosphere that come from spray cans, refrigerants, and air conditioners.Once they reach the ozone layer, they will react with the ozone molecules.This will result in a reduction of the ozone layer. In the absence of ozone layer, there will be a direct exposure to ultraviolet rays of the Sun which can cause a variety of health-related issues such as cancer, mutations, etc.

Answer: Option C. -> glaciers
:
C
Out of the 3% of the fresh water found on the Earth's surface,  majority is found in the form of glaciers. Almost 90% of the fresh water of Earth's ice mass is in Antarctica. The rivers and underground water are fresh water bodies while ocean water is saline.

Answer: Option A. -> True
:
A
Soil formation is influenced by physical, chemical and biological processes. Physical factors like water and wind, chemical processes like hydration, biological factors like living organisms do influence soil formation.