Aspirant Academy

Science and Technology

Predicted Questions with Model Answers

Chemistry: Atomic Structure, Metals & Non-Metals, Ores & Alloys, Acids/Bases/pH, Drugs, Pesticides, Carbon Compounds, Fuels, Radioactivity, Green Chemistry

Paper II · Unit 2 Section 11 of 13 0 PYQs 28 min
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Predicted Questions with Model Answers

Q1 (5 marks — 50 words): What are isotopes? Give two examples and state one practical application of each.

Model Answer:

Isotopes are atoms of the same element with identical atomic number (Z) but different mass numbers (A) — they differ in neutron count. Example 1: Carbon-14 (Z=6, A=14, half-life 5,730 years) — used in radiocarbon dating to determine age of organic archaeological specimens. Example 2: Iodine-131 (Z=53, A=131, half-life 8 days) — used in thyroid cancer diagnosis and treatment via targeted radiation.

Q2 (5 marks — 50 words): Distinguish between analgesics, antiseptics, and disinfectants with one example each.

Model Answer:

Analgesics relieve pain without causing loss of consciousness — example: Paracetamol (also antipyretic). Antiseptics are applied on living tissues (wounds, skin) to prevent microbial infection — example: Dettol (chloroxylenol). Disinfectants destroy microbes on non-living surfaces (instruments, floors) and are too toxic for skin — example: Phenol (carbolic acid), the first surgical disinfectant used by Joseph Lister in 1867.

Q3 (5 marks — 50 words): What is vulcanisation of rubber? Who discovered it and what are its benefits?

Model Answer:

Vulcanisation is the process of heating natural rubber with sulphur (3–5%) at 140–180°C to create cross-links between polyisoprene chains. Discovered by Charles Goodyear (1839) in the USA. Benefits: (1) improved tensile strength and elasticity; (2) resistance to extreme temperatures (−40°C to +120°C); (3) reduced stickiness; (4) water resistance. Essential for tyres, tubes, seals, footwear, and industrial gaskets.

Q4 (5 marks — 50 words): What is green chemistry? State any four of its 12 principles.

Model Answer:

Green chemistry (Anastas & Warner, 1998) designs chemical products and processes to reduce or eliminate hazardous substances. Four principles: (1) Waste Prevention — better to prevent than treat; (2) Atom Economy — maximise raw material in product; (3) Renewable Feedstocks — use plant-based/agricultural sources; (4) Catalysis — use catalytic rather than stoichiometric amounts to reduce waste and energy use. India's National Green Hydrogen Mission (2023, Rs 19,744 crore) embodies green chemistry principles.

Q5 (5 marks — 50 words): Differentiate between nuclear fission and nuclear fusion with examples.

Model Answer:

Nuclear fission: A heavy nucleus (U-235 or Pu-239) splits into two lighter nuclei on neutron bombardment, releasing ~200 MeV energy; chain reaction powers nuclear reactors and bombs. Nuclear fusion: Light nuclei (deuterium + tritium) combine at ~100 million °C to form helium, releasing ~17.6 MeV; powers the Sun; no long-lived radioactive waste. ITER (France, India member) is building a commercial fusion reactor targeting first plasma 2025.

Q6 (5 marks — 50 words): What is pH? State the pH of blood, stomach acid, and seawater, and explain the importance of pH in daily life.

Model Answer:

pH = −log[H⁺] measures hydrogen ion concentration on a 0–14 scale. Below 7 = acidic; 7 = neutral; above 7 = alkaline. Key values: blood = 7.35–7.45 (acidosis/alkalosis if outside range); stomach acid = 1.5–2.0 (HCl); seawater = 8.1 (ocean acidification threat from CO₂). Daily importance: pH affects tooth decay (below 5.5), soil fertility (6.5–7.0 ideal), water safety, and medicine formulation.