UPSC Static Quiz – Environment : 13 December 2025

Solution: A

Only Statement 2 is correct.

The higher amounts of waste increases the rates of decomposition and O2 consumption, thereby decreases the DO content of water. The demand for O2 is directly related to increasing input of organic wastes and is expressed as biological oxygen demand (BOD) of water.

Water pollution by organic wastes is measured in terms of Biochemical Oxygen Demand (BOD). BOD is the amount of dissolved oxygen needed by bacteria in decomposing the organic wastes present in water. It is expressed in milligrams of oxygen per litre of water.

The higher value of BOD indicates low DO content of water. Since BOD is limited to biodegradable materials only. Therefore, it is not a reliable method of measuring pollution load in water.

Chemical oxygen demand (COD) is a slightly better mode used to measure pollution load in water.

It is the measure of oxygen equivalent of the requirement of oxidation of total organic matter (i.e. biodegradable and non-biodegradable) present in water.

Solution: A

Statement 1 is incorrect.

Nitrates not only affect surface water but also pollute groundwater sources.

Nitrous oxide (N2O) gas should not be confused with nitric oxide (NO) or nitrogen dioxide (NO2). Neither nitric oxide nor nitrogen dioxide are greenhouse gases. Nitrous oxide is a greenhouse gas.

Nitrogen particles make up the largest fraction of PM2.5, the class of pollutants closely linked to cardiovascular and respiratory illness

Though agriculture remains the largest contributor to nitrogen emissions, the non-agricultural emissions of nitrogen oxides and nitrous oxide are growing rapidly, with sewage and fossil-fuel burning — for power, transport and industry — leading the trend.

Solution: C

• Sea weeds are macroscopic algae, which means they have no differentiation of true tissues such as roots, stems and leaves.
• They grow in shallow coastal waters wherever a sizable sub-strata is available.
• Seaweeds are important as food for humans, feed for animals, and fertilizer for plants.
• Seaweeds are used as a drug for goiter treatment, intestinal and stomach disorders.
• Products like agar-agar and alginates, iodine which are of commercial value, are extracted from seaweeds.
• By the biodegradation of seaweeds, methane like economically important gases can be produced in large quantities.
• They are potential indicators of pollution in coastal ecosystem, particularly heavy metal pollution due to their ability to bind and accumulate metals strongly.
• Rotting seaweed is a potent source of hydrogen sulfide, a highly toxic gas.

Solution: A

The Formation of Smog

• Photochemical smog (smog) is a term used to describe air pollution that is a result of the interaction of sunlight with certain chemicals in the atmosphere.
• One of the primary components of photochemical smog is ozone.
• While ozone in the stratosphere protects earth from harmful UV radiation, ozone on the ground is hazardous to human health.
• Ground-level ozone is formed when vehicle emissions containing nitrogen oxides (primarily from vehicle exhaust) and volatile organic compounds (from paints, solvents, printing inks, petroleum products, vehicles, etc.) interact in the presence of sunlight.

Solution: D

Indoor air pollution refers to the physical, chemical, and biological characteristics of air in the indoor environment within a home, building, or an institution or commercial facility.

Other than nitrogen dioxide, carbon monoxide, and lead, there are a number of other pollutants that affect the air quality in an enclosed space.

Volatile organic compounds originate mainly from solvents and chemicals. The main indoor sources are perfumes, hair sprays, furniture polish, glues, air fresheners, moth repellents, wood preservatives, and many other products used in the house.

Tobacco smoke generates a wide range of harmful chemicals and is known to cause cancer.

Pesticides, if used carefully do not cause too much harm to the indoor air.

Biological pollutants include pollen from plants, mite, hair from pets, fungi, parasites, and some bacteria. Most of them are allergens and can cause asthma, hay fever, and other allergic diseases.

Formaldehyde is a gas that comes mainly from carpets, particle boards, and insulation foam. It causes irritation to the eyes and nose and may cause allergies in some people.

Asbestos is mainly a concern because it is suspected to cause cancer.

Radon is a gas that is emitted naturally by the soil. Due to modern houses having poor ventilation, it is confined inside the house causing harm to the dwellers.