Why Correct: Chlorofluorocarbons release chlorine atoms that catalytically destroy ozone molecules in the stratosphere.
Distractor Analysis: Carbon monoxide primarily causes indoor air pollution and binds with hemoglobin. Carbon dioxide drives global warming through the greenhouse effect. Mercuric oxide is a toxic compound used in batteries and pigments.
Takeaway: The Montreal Protocol successfully phased out 99% of ozone-depleting substances, preventing an estimated 2 million skin cancer cases annually by 2030.

Why Correct: PVC stands for Poly Vinyl Chloride, a synthetic polymer made from vinyl chloride monomers through addition polymerization.
Distractor Analysis: Phospho Vinyl Chloride does not exist as a standard plastic material. Poly Vinyl Carbonate is not a commercially significant polymer. Phospho Vanadium Chloride is an inorganic compound unrelated to plastics manufacturing.
Takeaway: PVC is the world's third-most widely produced synthetic plastic polymer, after polyethylene and polypropylene, with applications ranging from pipes to medical devices.

Why Correct: DDT spraying contaminates air through drift during application, soil through direct deposition and persistence, and water through runoff and leaching into groundwater and surface water bodies.
Distractor Analysis: Air-only pollution ignores DDT's persistence in soil for years and its mobility into water systems. Air-and-soil-only misses aquatic contamination through agricultural runoff. Air-and-water-only overlooks direct soil absorption and long-term soil residue.
Takeaway: DDT's environmental persistence and bioaccumulation in food chains led to its ban in most countries under the Stockholm Convention on Persistent Organic Pollutants.

Why Correct: Chlorine nitrate (ClONO2) forms when chlorine monoxide reacts with nitrogen dioxide in polar stratospheric clouds, acting as a temporary reservoir that releases chlorine atoms when sunlight returns in spring, catalysing ozone destruction.
Distractor Analysis: Nitrogen dioxide contributes to photochemical smog and acid rain but helps form chlorine nitrate. Sulphur dioxide causes acid rain and volcanic cooling effects. Freon is a trade name for chlorofluorocarbons (CFCs) like CFC-12 that release chlorine atoms when broken down by UV radiation.
Takeaway: The Antarctic ozone hole peaks in September–October, with the Montreal Protocol (1987) phasing out CFCs, leading to gradual ozone layer recovery projected by mid-21st century.

Why Correct: Peroxyacetyl nitrate (PAN) disrupts the Hill reaction by oxidising thylakoid membranes in chloroplasts, specifically inhibiting photosystem II's electron transport chain that splits water during photosynthesis.
Distractor Analysis: Nitrogen monoxide (nitric oxide) regulates plant growth and defence but causes photochemical smog with VOCs. Ultraviolet rays damage DNA and proteins but are not atmospheric pollutants. Hydrocarbons like methane and VOCs contribute to ozone formation but do not directly inhibit the Hill reaction.
Takeaway: PAN forms when hydrocarbons and nitrogen oxides react in sunlight, causing plant damage visible as silvering or bronzing on leaf undersides, particularly affecting sensitive crops like beans and tomatoes.

Why Correct: Compressed natural gas (CNG) produces significantly lower emissions of particulate matter, carbon monoxide, and sulfur oxides compared to conventional fuels like petrol and diesel.
Distractor Analysis: Petrol and diesel combustion generates higher levels of nitrogen oxides and particulate matter that contribute to urban air pollution. Alcoholic fuels like ethanol or methanol can reduce emissions but require different engine modifications and are less commonly adopted for auto rickshaws than CNG.
Takeaway: Other alternative vehicle fuels include liquefied petroleum gas (LPG), biodiesel, hydrogen fuel cells, and electric batteries, each with different emission profiles and infrastructure requirements.

Why Correct: Ozone generators oxidize organic pollutants, bacteria, and odors in enclosed underground systems through its strong disinfectant properties.
Distractor Analysis: Hydrogen peroxide serves as a surface disinfectant and bleaching agent but requires careful handling in confined spaces. Oxygen supports combustion and respiration but does not purify air. None of the above ignores established ozone-based air purification systems in metro networks.
Takeaway: Ozone's high oxidation potential (2.07 V) makes it effective against volatile organic compounds and microorganisms, though it must be carefully controlled to avoid respiratory irritation.

Why Correct: Nitrogen fixation converts atmospheric N2 gas into ammonia, nitrates, or other usable nitrogen compounds through biological, industrial, or natural processes.
Distractor Analysis: Liquefaction of nitrogen is a physical process for storage and transport at cryogenic temperatures. Manufacture of nitrogen from air refers to fractional distillation for industrial N2 gas production. Conversion of nitrogen into nitric acid is one specific industrial fixation method via the Ostwald process.
Takeaway: Biological nitrogen fixation occurs via Rhizobium bacteria in legume root nodules, using nitrogenase enzyme that requires anaerobic conditions and is inhibited by oxygen.

Why Correct: Radiocarbon dating measures C-14 decay in once-living organic materials like fossils, which absorbed atmospheric carbon during life.
Distractor Analysis: Rocks typically use radiometric dating with longer-lived isotopes like uranium-lead. Monuments made of stone require other dating methods. Soil contains mixed organic and inorganic materials, making C-14 dating unreliable.
Takeaway: C-14 dating works for organic remains up to ~50,000 years; older samples use potassium-argon or uranium-lead dating.