PRELIMS PREVIOUS YEAR QUESTIONS
Q.1 ) Consider the following statements regarding mercury pollution: UPSC (2023)
- Gold mining activity is a source of mercury pollution in the world.
- Coal-based thermal power plants cause mercury pollution.
- There is no known safe level of exposure to mercury.
How many of the above statements are correct?
- Only one
- Only two
- All three
- None
Answer: B
Explanation:
- Statement 1: Gold mining activity is a source of mercury pollution in the world — Correct.
- Artisanal and small-scale gold mining (ASGM) is the largest source of anthropogenic mercury emissions globally, as mercury is used to extract gold from ore.
- Statement 2: Coal-based thermal power plants cause mercury pollution — Correct.
- Coal contains trace amounts of mercury, which is released into the atmosphere when coal is burned in thermal power plants, contributing to mercury emissions.
- Statement 3: There is no known safe level of exposure to mercury — Incorrect.
- While mercury is highly toxic and exposure should be minimized, regulatory agencies like WHO and EPA set threshold limits for safe exposure to mercury. Hence, the claim of “no known safe level” is not entirely accurate.
Q.2) The water pollution in a river is measured by the dissolved amount of: UPSC (2018)
- Chlorine
- Ozone
- Nitrogen
- Oxygen
Answer: D
Explanation:
- The dissolved oxygen (DO) level in water is a key indicator of water quality and pollution.
- When organic pollutants (like sewage, agricultural runoff) enter water bodies, they increase the Biological Oxygen Demand (BOD) because microbes consume oxygen to break down organic matter.
- As a result, dissolved oxygen levels decrease, which can harm aquatic life.
- A high DO level usually indicates good water quality, while low DO suggests high pollution and poor water quality.
- Chlorine, ozone, and nitrogen are not used as direct indicators of water pollution in rivers.
Q.3) In the context of solving pollution problems, what is/are the advantage/advantages of bioremediation technique? UPSC (2017)
- It is a technique for cleaning up pollution by enhancing the same biodegradation process that occurs in nature.
- Any contaminant with heavy metals such as cadmium and lead can be readily and completely treated by bioremediation using microorganisms.
- Genetic engineering can be used to create microorganisms specifically designed for bioremediation.
Select the correct answer using the code given below:
- 1 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Answer: C
Explanation:
- Statement 1: Correct.
- Bioremediation leverages and enhances the natural biodegradation process by microorganisms to clean up pollutants in soil, water, and air. It is an eco-friendly and cost-effective technique.
- Statement 2: Incorrect.
- Heavy metals like cadmium and lead are not biodegradable. Microorganisms cannot completely break them down; they can only immobilize, adsorb, or transform them to less toxic forms. Hence, heavy metals cannot be readily and completely treated by bioremediation.
- Statement 3: Correct.
- Genetic engineering can indeed create specialized microorganisms with enhanced capabilities to degrade specific pollutants, improving the efficiency of bioremediation.
Q.4) Which of the following can be found as pollutants in the drinking water in some parts of India? UPSC (2013)
- Arsenic
- Sorbitol
- Fluoride
- Formaldehyde
- Uranium
Select the correct answer using the codes given below:
- 1 and 3 only
- 2, 4 and 5 only
- 1, 3 and 5 only
- 1, 2, 3, 4 and 5
Answer: C
Explanation:
- Arsenic (1): Present — Correct.
- Arsenic contamination is a major issue in groundwater in parts of West Bengal, Bihar, Assam, and Uttar Pradesh. It causes serious health issues like skin lesions and cancer.
- Sorbitol (2): Not Present — Incorrect.
- Sorbitol is a sugar alcohol used as a sweetener in food products. It is not a known water pollutant in India.
- Fluoride (3): Present — Correct.
- Fluoride contamination is common in Rajasthan, Andhra Pradesh, and Telangana, causing dental and skeletal fluorosis.
- Formaldehyde (4): Not Present — Incorrect.
- Formaldehyde is used industrially and in laboratories; it is not reported as a groundwater contaminant in India.
- Uranium (5): Present — Correct.
- Uranium contamination has been reported in groundwater in parts of Punjab and Haryana, raising concerns over kidney damage and cancer risk.
Q.5) Acid rain is caused by the pollution of environment by: UPSC (2013)
- Carbon dioxide and nitrogen
- Carbon monoxide and carbon dioxide
- Ozone and carbon dioxide
- Nitrous oxide and sulphur dioxide
Answer: D
Explanation:
- Acid rain is formed when sulphur dioxide (SO₂) and oxides of nitrogen (NOₓ: NO and NO₂) are released into the atmosphere due to burning of fossil fuels, industrial emissions, and vehicular exhaust.
- These gases react with water vapor, oxygen, and other chemicals in the atmosphere to form sulphuric acid (H₂SO₄) and nitric acid (HNO₃).
- These acids fall to the ground as precipitation — rain, snow, sleet — making it acidic.
- The other options like carbon dioxide, carbon monoxide, and ozone contribute to greenhouse effect, global warming, or photochemical smog, but not significantly to acid rain.
Thus, nitrous oxide (NOₓ) and sulphur dioxide (SO₂) are the primary contributors to acid rain.