Q40. Henri Becquerel discovered which phenomenon?
[RRB NTPC CBT-I (4 February 2021, Shift 2)]
(A) Ultraviolet radiation
(B) Infrared radiation
(C) X-rays
(D) Spontaneous radioactivity
Answer: (D) Spontaneous radioactivity
Explanation: Becquerel observed that uranium salts affected photographic plates even without exposure to light. This established spontaneous radioactivity. Wilhelm Röntgen is associated with the discovery of X-rays, an entirely different historical experiment.
Q39. The mineral carnotite is an important source of which element?
[SSC MTS 2020 exam (held 22 October 2021, Shift 1)]
(A) Copper
(B) Zinc
(C) Uranium
(D) Iron
Answer: (C) Uranium
Explanation: Carnotite is a hydrated potassium uranium vanadate mineral and therefore an ore of uranium, often associated with vanadium. Uranium isotopes underpin nuclear fuel cycles, while the mineral itself is not used directly as reactor fuel.
Q38. Why are some Indian nuclear reactors subject to IAEA safeguards while other reactors are not?
[UPSC Civil Services Preliminary Examination (2020)]
(A) They operate on thorium rather than uranium
(B) They use imported rather than domestically sourced uranium
(C) They are privately rather than publicly operated
(D) They are foreign-owned
Answer: (B) They use imported rather than domestically sourced uranium
Explanation: Under India’s civil nuclear agreements, designated civilian installations using imported fuel are placed under International Atomic Energy Agency safeguards. The distinction reflects fuel-supply and safeguards commitments rather than an intrinsic difference in the science of fission.
Q37. Which assertion about neutrons is false?
[UPSC CDS-II General Knowledge (2020)]
(A) A neutron has almost a proton’s mass
(B) A neutron is electrically neutral
(C) Neutrons occur within atomic nuclei
(D) Neutrons orbit nuclei like electrons
Answer: (D) Neutrons orbit nuclei like electrons
Explanation: Neutrons are nucleons that reside within most atomic nuclei alongside protons. Their electric charge is zero, and their mass is close to a proton’s. Electrons, rather than neutrons, occupy atomic electronic states outside the nucleus.
Q36. What was the weapon codenamed “Little Boy”?
[UPSC CDS General Knowledge (8 November 2020)]
(A) A fission bomb used at Hiroshima
(B) A fusion bomb used at Nagasaki
(C) The first US test device
(D) North Korea’s first test device
Answer: (A) A fission bomb used at Hiroshima
Explanation: Little Boy was the uranium-based fission weapon dropped on Hiroshima on 6 August 1945. It derived its explosive energy from an uncontrolled nuclear chain reaction. The Nagasaki bomb, Fat Man, used a different plutonium fission design.
Q35. Which mineral is associated with fuel extraction for nuclear power stations?
[UPSC NDA-I General Ability Test (2019)]
(A) Bauxite
(B) Quartz
(C) Feldspar
(D) Pitchblende
Answer: (D) Pitchblende
Explanation: Pitchblende, also known as uraninite, is a uranium-rich mineral. Uranium recovered from ores can be processed into nuclear fuel. Bauxite chiefly yields aluminium, while quartz and feldspar are common silicate minerals.
Q34. What is the central operating principle of a commercial nuclear reactor?
[UPSC NDA-I General Ability Test (2019)]
(A) Uncontrolled fusion
(B) Controlled fusion
(C) Uncontrolled fission
(D) Controlled fission
Answer: (D) Controlled fission
Explanation: Commercial nuclear reactors sustain controlled fission chain reactions. Neutrons split fissile nuclei, releasing heat and further neutrons, while control systems regulate reactivity. Fusion remains primarily a research technology rather than the standard basis of commercial reactors.
Q33. About joining the Nuclear Suppliers Group, consider:
1. Membership supports access to nuclear technologies.
2. It automatically confers NPT membership.
Which is correct?
[UPSC Civil Services Preliminary Examination (2018)]
(A) 1 only
(B) 2 only
(C) Both
(D) Neither
Answer: (A) 1 only
Explanation: The Nuclear Suppliers Group coordinates controls on nuclear-related exports and may facilitate legitimate technology trade among participating states. NSG participation does not automatically make a country a party to the separate Nuclear Non-Proliferation Treaty.
Q32. India’s ratification of the IAEA Additional Protocol chiefly relates to which consequence?
[UPSC Civil Services Preliminary Examination (2018)]
(A) Certain civilian reactors becoming subject to IAEA safeguards
(B) All military nuclear sites being opened automatically
(C) Automatic NSG membership
(D) Guaranteed uranium imports from any country
Answer: (A) Certain civilian reactors becoming subject to IAEA safeguards
Explanation: The Additional Protocol expands information and access arrangements associated with safeguards for designated civilian nuclear facilities. It does not automatically place military installations under safeguards, create NSG membership or confer unrestricted rights to purchase nuclear fuel.
Q31. Which fallout isotopes may enter humans through food chains and cause physiological harm?
[UPSC CDS-II General Knowledge (2017)]
(A) Strontium-90 only
(B) Iodine-131 only
(C) Caesium-137 only
(D) All three listed isotopes
Answer: (D) All three listed isotopes
Explanation: Radioactive strontium-90 can accumulate in bones, iodine-131 concentrates in the thyroid, and caesium-137 behaves chemically somewhat like potassium. These radionuclides can enter food and water after contamination and expose internal organs to ionising radiation.
