Physics & chemistry in everyday life

Answer: (c) Only three

In a lithium-ion cell the cathode is a metal-oxide material built from lithium with nickel, cobalt (and manganese), as in the common NMC type. Graphite is the anode material, not part of the cathode. So three of the four elements make up cathodes.

• ✓ I Cobalt is one of the metals in the active cathode material.
• ✗ II Graphite forms the anode of the cell, not the cathode.
• ✓ III Lithium is a cathode mineral (the IEA lists lithium, nickel, cobalt and manganese for the cathode).
• ✓ IV Nickel is a main cathode metal; nickel-rich cathodes are a key trend in EV batteries.

Remember · EV battery cathode: lithium with nickel, cobalt (and manganese). Anode: graphite.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (c) All the three

All three contain plastic. Cigarette filters are made mainly of cellulose acetate fibres, which are microplastics; many eyeglass lenses are plastic (for example CR-39 and polycarbonate); and tiny plastic particles are shed by car tyres as they wear.

• ✓ I The WHO Framework Convention on Tobacco Control Secretariat says cigarette filters are mainly composed of microplastics known as cellulose acetate fibres.
• ✓ II Many spectacle lenses are made of plastic: a peer-reviewed study of spectacle lens materials covers CR-39, polycarbonate and Trivex, and calls CR-39 lenses the most basic form of plastic lenses.
• ✓ III IUCN counts particles worn off car tyres among the tiny plastic particles that reach the oceans.

Remember · Cigarette filters (cellulose acetate), eyeglass lenses (CR-39, polycarbonate) and car tyres (which shed microplastics) all contain plastic.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink · Report an error

Answer: (b) Only two

Coal gasification turns coal into syngas, which is then converted into fuels and chemicals. India's Ministry of Coal lists ethanol among these products and describes the Talcher plant converting syngas to ammonia and then urea. Nitroglycerine is made by nitrating glycerine with nitric and sulphuric acids and is not one of the coal-gasification products, so only two of the three qualify.

• ✓ I The Ministry of Coal includes ethanol among the liquid fuels made from syngas and notes that a policy change is under way to include ethanol from the coal gasification route.
• ✗ II Nitroglycerine (glyceryl trinitrate) comes from nitrating glycerine with mixed nitric and sulphuric acids; it is not a syngas product.
• ✓ III At Talcher, coal blended with pet-coke is gasified to syngas, converted into ammonia and then into urea.

Remember · Coal gasification gives syngas, then methanol, ethanol, ammonia and urea (Talcher fertiliser plant). Nitroglycerine comes from glycerine and nitrating acids, not from syngas.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (a) Both Statement II and Statement III are correct and both of them explain Statement I

Both Statement II and Statement III are correct, and both explain Statement I. A large surface area lets activated carbon hold heavy metals and other pollutants on its surface, and because it can be made cheaply from carbon-rich waste, it becomes an attractive tool for cleaning effluents.

• ✓ II Activated carbon is highly porous, with a very large surface area and strong adsorption capacity. Pollutants stick to that surface (adsorption), which is exactly how it strips heavy metals from wastewater. This explains why it removes pollutants (Statement I).
• ✓ III Farm and other carbon-rich wastes are the usual raw material for activated carbon, and the process is simple and cheap. This low cost explains why it is 'attractive' as a treatment tool (Statement I).
• ✗ (b) This option says only one of II and III explains Statement I. But the ability to adsorb (II) explains the 'good' part and the cheap, waste-based supply (III) explains the 'attractive' part, so both explain it.
• ✗ (d) Both statements are supported by published research on biomass-derived activated carbon, so 'neither is correct' fails.

Remember · Activated carbon = porous, huge surface area, strong adsorbent, cheaply made from carbon-rich waste; hence widely used to clean effluents.

Question and answer: UPSC's official GS Paper I (2025, 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

Both statements are correct. Rare earth compounds such as europium and yttrium oxides act as phosphors, the light-emitting coatings that give colour in television and computer screens, so their luminescent property is exactly why they are used in displays.

• ✓ Statement-I IREL (India) Limited, a Department of Atomic Energy undertaking, lists television screens, computers and monitor displays among rare-earth uses; europium and yttrium oxides produce the red colour in television screens.
• ✓ Statement-II Rare earths have luminescent properties, and several (europium, terbium) are used as phosphors. That is why they light up screens, so this statement explains Statement-I.

Remember · Europium and yttrium oxides are rare-earth phosphors: their luminescence gives red (and, with europium, blue) colour in TV and phone screens.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (a) silver iodide and potassium iodide

Artificial rain is made by cloud seeding: seed particles are added to a cloud so that rain can form, and Delhi has trialled it as an emergency measure against pollution episodes. India's IITM names silver iodide as the standard seeding agent for cold clouds, and UPSC's key pairs it with potassium iodide.

• ✓ (a) Both agents are iodides. IITM's CAIPEEX pages name silver iodide (AgI) as the ice-nucleating agent used in glaciogenic seeding; UPSC's key names potassium iodide as the second agent, which the IITM pages do not mention.
• ✗ (b) Silver nitrate replaces silver iodide here; the key's answer has both agents as iodides.
• ✗ (c) Potassium nitrate replaces potassium iodide here; the key's answer has both agents as iodides.
• ✗ (d) Silver nitrate and potassium chloride replace both iodides.

Remember · Cloud seeding uses iodide salts, chiefly silver iodide (with potassium iodide in the key), to trigger rain.

Question and answer: UPSC's official GS Paper I (2025, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error