Answer: Option D. -> All of these
:
D
Although there are natural sources of sulphur dioxide (accounting for 35-65% of the total sulphur dioxide emissions) such as volcanoes, most anthropogenic sulphur dioxide is produced by burning fuels containing sulphur or by roasting metal sulphide ores. Thermal power plants burning high-sulphur coal or heating oil are generally the main sources of sulphur dioxide emissions worldwide, followed by industrial boilers and nonferrous metal smelters. Emissions from domestic coal burning and from vehicles can also contribute to high concentrations of sulphur dioxide.

Answer: Option B. -> Radioactive substances
:
B
Solid wastes that we generate in the environment can be categorised into three groups:
1. Biodegradable wastes are those wastes that are capable of being decomposed in a reasonable amount of time by bacteria or other living organisms and thus, do not cause pollution. Examples include human and animal waste, biofertilisers, kitchen waste etc. 
2. Recyclable wastes are those that can be converted to reusable material. Glass, cardboard boxes, paper products, etc. are examples. 
3. Non-biodegradable wastes those that can not be broken down into their base compounds by microorganisms, air, moisture or soil in a reasonable amount of time. Radioactive elements, plastic, metal scraps etc. are non-biodegradable.

Answer: Option C. -> Release of SO₂ and NO from burning fossil fuels
:
C

Acid rain is caused by a chemical reaction that begins when compounds like sulphur dioxide and nitrogen oxides are released into the air. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen and other chemicals to form more acidic pollutants to precipitate down as acid rain.

Answer: Option A. -> Chipko movement
:
A and B

In the 1970s, an organised resistance to the destruction of forests spread throughout India and came to be known as the Chipko movement. The Chipko Movement in the state of Uttarakhand inspired the villagers of the Uttara Kannada district of the state of Karnataka in southern India to launch a similar movement to save their forests. This came to be known as the Appiko movement. Swachh Bharat Abhiyan was a mass movement across India started on October 2, 2014 to remove garbage and clean India. The “Ganga Action Plan” (GAP) was launched for immediate reduction of pollution load on the river Ganga in December, 1984 on the basis of a survey on the Ganga basin, carried out by the Central Pollution Control Board in 1984.
 

Answer: Option A. -> Water logging
:
A, B, and C

Irrigation without proper drainage of water leads to waterlogging in the soil. Besides affecting the crops, waterlogging draws salt to the surface of the soil. The salt then gets deposited as a thin crust on the land surface or starts collecting at the roots of the plants. This increased salt content inhibits the growth of crops and is extremely damaging to agriculture.

Answer: Option D. -> Both A and R are false
:
D

UV radiation does not cause photodissociation of ozone into O₂ and O. Instead, it takes part in the formation of ozone in two steps.

O₂ ---> O + O
O₂ + O ---> O₃

Due to certain careless human activities, the ozone layer in the stratosphere has been thinning down in certain areas, which are being known as "ozone hole". The ozone hole has been resulting in rain failure, increased incoming radiation, cancers and a reduction in crop production. Global warming and climate changes are mainly caused due to an increase in the amounts of greenhouse gases in the atmosphere.

Answer: Option A. -> Ozone layer
:
A

The ozone layer is a natural layer of gas in the upper atmosphere which protects humans and other living things from the harmful ultraviolet (UV) rays of the sun. This ozone layer performs the essential task of filtering out most of the sun's biologically harmful UV radiation.

Answer: Option D. -> Many of the birds' eggs laid, did not hatch
:
D

Biomagnification refers to an increase in concentration of a toxicant at successively higher trophic levels. This happens because a toxic substance accumulated by an organism cannot be metabolised or excreted and is thus, passed on in the food chain. DDT biomagnification occurs in aquatic food chains. If the concentration of DDT in water for instance, is 0.003 ppb (ppb = parts per billion) in water, that ultimately reaches 25 ppm (ppm = parts per million) in fish-eating birds, through biomagnification. High concentration of DDT disturbs calcium metabolism in birds which causes thinning of egg shells and their premature breaking.

Answer: Option B. -> Both A and R are true but R is not the correct explanation for A
:
B

An element subject to spontaneous degeneration of its nucleus accompanied by the emission of alpha particles, beta particles or gamma rays is called a radioactive element. Nuclear fallout refers to the radioactive particles that fall on to the earth as a result of a nuclear explosion. Fallout particles vary in size from thousandths of a millimeter to several millimeters. Much of this material falls directly back down close to ground where the explosion happened within several minutes after the explosion, but some get dispered by winds over long distances. The fallout usually gets suspended in the atmosphere, 6 to 7 km above the earth's surface. These radionuclides also often settle down by rain and get mixed with soil and water. From there, they can easily enter the food chain and finally get deposited in the human body where they cause serious health hazards.

 

Answer: Option A. -> DDT is biodegradable and does not undergoes biomagnification
:
A

Biomagnification is the process by which toxic substances which cannot be metabolised by the body, start becoming more and more concentrated at successive trophic levels. DDT was once, used extensively as a pesticide and was sprayed on crops to kill insects. However, it has been noticed that through run off from fields, DDT enters streams and lakes, and enters the food chain of aquatic plants and animals. Because DDT is non-biodegradable, it keeps accumulating at toxic levels in living bodies.