Nuclear Chemistry and Radioactivity – NDA Chemistry PYQs

Solve NDA Chemistry previous-year questions on Nuclear Chemistry with detailed solutions and explanations.

Chapter-wise PYQs • Concept-based explanations • Exam insights

NDA 2021-II

Q. 1. Which one of the following elements’ isotopes is used in the treatment of cancer?

(a) Iodine

(b) Sodium

(d) Uranium

Answer: (c) Cobalt

Explanation: Cobalt-60 (⁶⁰Co) emits gamma radiation and is used in radiotherapy (cobalt therapy) to treat cancer. Iodine-131 is used to treat thyroid disorders. Uranium is used as nuclear fuel, not in medical treatment. Concept Tested: Cancer treatment isotope – Cobalt-60

★ JOVIK Exam Insight: Co-60 = cancer radiotherapy. I-131 = thyroid treatment. NDA tests both medical radioisotopes.

NDA 2019-I

Q. 2. Which one of the following minerals is used as a fuel in nuclear power stations (Nuclear Power Station)?

(a) Bauxite

(b) Quartz

(d) Pitchblende

Answer: (d) Pitchblende

Explanation: Pitchblende (uraninite, primarily UO₂) is the main ore of uranium. Uranium from pitchblende is used as nuclear fuel in nuclear power stations. Bauxite is Al ore. Quartz is SiO₂. Feldspar is a silicate mineral. Concept Tested: Nuclear fuel mineral – pitchblende (uranium ore)

NDA 2018-I

Q. 3. Which one of the following metals is alloyed with sodium to transfer heat in a nuclear reactor?

(a) Potassium

(b) Calcium

(d) Strontium

Answer: (a) Potassium

Explanation: In fast breeder reactors, a sodium-potassium alloy (NaK) is used as a liquid metal coolant to transfer heat. NaK remains liquid at room temperature and has excellent heat transfer properties. Concept Tested: NaK alloy – heat transfer coolant in nuclear reactors

NDA 2015-II

Q. 4. Which of the following statements regarding heavy water are correct?

1. It is extensively used as a moderator in nuclear reactors

2. It cannot be used in exchange reaction to study reaction mechanism

3. Viscosity of heavy water is relatively smaller than that of ordinary water

4. The dielectric constant of heavy water is smaller than that of ordinary water

Select the correct answer using the code given below:

(a) 1 and 2

(b) 2 and 3

(d) 1 and 4

Answer: (d) 1 and 4

Explanation: Statement 1: Correct – heavy water is used as a moderator in CANDU nuclear reactors. Statement 2: Incorrect – heavy water CAN be used in exchange reactions (isotopic labelling in kinetic studies). Statement 3: Incorrect – heavy water has HIGHER viscosity than ordinary water. Statement 4: Correct – the dielectric constant of D₂O (~77.9 at 25°C) is slightly lower than H₂O (~78.4). So 1 and 4 are correct. Concept Tested: Properties of heavy water – moderator, higher viscosity, lower dielectric constant

NDA 2013-I

Q. 5. The phenomenon of radioactivity was discovered by

(a) Marie Curie

(b) Pierre Curie

(d) J. J. Thomson

Answer: (c) Henri Becquerel

Explanation: Henri Becquerel discovered radioactivity in 1896 by observing that uranium salts emit penetrating radiation (without exposure to light). Marie and Pierre Curie later studied radioactivity extensively and discovered polonium and radium, but the original discovery of radioactivity belongs to Becquerel. Concept Tested: Discovery of radioactivity – Henri Becquerel (1896)

NDA 2009-I

Q. 6. Which one among the following is used as a moderator in nuclear reactors?

(a) Ozone

(b) Heavy hydrogen

(d) Hydrogen peroxide

Answer: (c) Heavy water

Explanation: Heavy water (D₂O, deuterium oxide) is used as a moderator in CANDU-type nuclear reactors. A moderator slows down fast neutrons to thermal (slow) neutrons, which are more efficient at sustaining nuclear fission. Ordinary water is also used as a moderator in most light-water reactors. Concept Tested: Nuclear reactor moderator – heavy water (D₂O)