Pollution & waste

Answer: (d) 1, 2 and 3

PFAS are man-made fluorinated chemicals used for non-stick, stain-proof and grease-proof products. Their carbon–fluorine bonds make them extremely persistent ('forever chemicals'), so they spread through water, food and packaging and build up in the bodies of people and animals. All three statements hold.

• ✓ 1. PFAS turn up in drinking water, in foods such as fish and dairy, and in grease-resistant food packaging like fast-food wrappers and pizza boxes.
• ✓ 2. They are long-lasting chemicals whose components break down very slowly, so they persist in the environment.
• ✓ 3. Because they persist, many PFAS are found in the blood of people and animals worldwide, and some accumulate in the body over time.

Remember · PFAS = 'forever chemicals': very slow to break down, found in water, food and packaging, and accumulate in human and animal bodies.

Question and answer: UPSC's official GS Paper I (2024, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (a) Both Statement-I and Statement-II are correct and Statement-II explains Statement-I

The chewy part of most modern gum is not a natural tree gum but a synthetic 'gum base' made of polymers such as polyvinyl acetate, polyethylene and butyl rubber, which are plastics. Because that base does not biodegrade, spat-out gum stays on pavements for years and slowly breaks into microplastics, so the plastic base is exactly why gum is counted as a pollutant.

• ✓ Statement-I Discarded gum is treated as litter, for example under the UK Clean Neighbourhoods and Environment Act, because a synthetic gum base does not biodegrade. It hardens on pavements, is costly to scrape off, and over years breaks into microplastic fragments.
• ✓ Statement-II Traditional gum used chicle, the latex of the sapodilla (zapota) tree. FSSAI's standard now permits both natural and synthetic gum bases, including synthetic rubber latex, synthetic resin and polyvinyl acetate, and US food rules list polyethylene, polyisobutylene and polyvinyl acetate. The plastic base is exactly why the gum lasts as litter, so Statement-II explains Statement-I.

Remember · Modern gum base = synthetic polymers (polyvinyl acetate, polyethylene, butyl rubber), i.e. plastic; old gum base = chicle from the zapota tree. Non-biodegradable, so gum litter becomes microplastic.

📘 Read it in NCERT: Class 12 Fundamentals of Human Geography, Ch 4 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2024, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (d) Wastewater treatment technologies

A membrane bioreactor (MBR) is a sewage and industrial-effluent treatment system. It joins the usual biological step, in which microbes break down organic waste, with fine membrane filtration that holds back solids and bacteria, so it produces clean, reusable water from a much smaller plant than conventional settling tanks.

• ✓ (d) The US EPA describes MBRs as a secondary-treatment technology for municipal wastewater that combines a suspended-growth biological reactor with microfiltration, removing nitrogen, phosphorus, bacteria and organic load.
• ✗ (c) Vaccine and biologics production uses bioreactors (fermenters) too, but the term 'membrane bioreactor' refers to the filtration-based wastewater process.
• ✗ (b) Nano drug-delivery systems use carriers such as liposomes and nanoparticles; they are not membrane bioreactors.

Remember · Membrane bioreactor = activated-sludge (microbial) treatment + membrane micro/ultrafiltration; compact, high-quality effluent fit for reuse. Used for sewage and industrial wastewater.

📘 Read it in NCERT: Class 12 Biology, Ch 8 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2024, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (d) Power plants using fossil fuels

The US Environmental Protection Agency names the burning of fossil fuels by power plants and other industrial facilities as the largest source of sulphur dioxide in the air. Metal extraction, volcanoes, locomotives and ships are only smaller sources.

• ✓ (d) Power plants that burn fossil fuels are the largest source of SO2 in the atmosphere according to the EPA.
• ✗ (c) Extracting metal from ore is an industrial process the EPA lists among the smaller sources.
• ✗ (b) Ships, like locomotives (option a), burn fuel with a high sulphur content, but the EPA counts them among the smaller sources.

Remember · Largest SO2 source: fossil-fuel burning by power plants and other industry. Smaller: extracting metal from ore, volcanoes, locomotives, ships.

Question and answer: UPSC's official GS Paper I (2024, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error