MCQs Based On Environment – (26)

Correct Option: 3. Peroxyacetyl nitrate (PAN)
Explanation: PAN is a secondary pollutant formed by the reaction of nitrogen oxides and hydrocarbons in the presence of sunlight. Unlike primary pollutants, it does not enter the environment directly but is produced through photochemical reactions in the atmosphere.

Correct Option: 1. DDT
Explanation: DDT (Dichloro-Diphenyl-Trichloroethane) is a synthetic pesticide that does not decompose naturally, making it a non-biodegradable pollutant. It accumulates in the food chain, causing long-term ecological damage.

Correct Option: 2. Quantitative pollutant
Explanation: Carbon dioxide occurs naturally in the environment, but it becomes a pollutant when its concentration exceeds the normal threshold. Hence, it’s called a quantitative pollutant.

A. Qualitative Pollutant
Definition:
Qualitative pollutants are man-made chemicals or materials that do not naturally occur in the environment.
Examples:
Pesticides (like DDT), fungicides, herbicides, CFCs.

B. Quantitative Pollutant
Definition:
Quantitative pollutants are substances that exist naturally in the environment, but become harmful when their concentration exceeds the threshold level.
Examples:
• Carbon dioxide (CO₂)
• Nitrogen oxides (NOₓ)
• Sulphur dioxide (SO₂)
CO₂ is naturally produced by respiration, decomposition, volcanic eruptions, etc. But human activities like burning of fossil fuels increase its levels beyond the safe threshold, making it a quantitative pollutant.

C. Biodegradable Pollutant
Definition:
These are pollutants that can be broken down into simpler, harmless substances by microorganisms.
Examples:
• Organic waste (e.g., food waste, sewage)
• Agricultural residue
• Paper
CO₂ is a gas, not an organic waste material, and microbes don’t break it down like they do with food or sewage. Also, gases are not classified as biodegradable/non-biodegradable.

D. Secondary Pollutant
Definition:
Secondary pollutants are not directly emitted into the environment. They form in the atmosphere by chemical reactions involving primary pollutants.
Examples:
• Ozone (O₃)
• Peroxyacetyl nitrate (PAN)
• Smog
CO₂ is a primary pollutant because it is directly released through burning fossil fuels and respiration. It is not formed by a reaction in the atmosphere, so it is not a secondary pollutant.

Correct Option: 4. Fungicides
Explanation: Qualitative pollutants are not naturally present in the environment and are introduced through human activities. Fungicides are synthetic chemicals used in agriculture and are not found naturally.

Correct Option: 1. Forest fire
Explanation: Forest fires are natural phenomena and can release large amounts of smoke, carbon monoxide, and particulate matter into the air, contributing to natural air pollution.