MCQs On Nuclei with answers NEET pdf
There is only a short time left for the exam. In such a situation, you must revise the important topic Class 12 Physics Chapter 13 Nuclei NEET Questions. Here are Experts who are telling Nuclei NEET MCQs are the most important in NEET. Which ones you should take a look at and start your Class 12 Nuclei MCQ Pdf Preparation.
1. The half-life period of radioactive material if its activity drops to (1/16)th of its initial value in 30 years is________
(a) 1.5 years
(b) 3.5 years
(c) 7.5 years
(d) 15 years
Answer: C) 7.5 years
Explanation: Activity becomes (1/2)⁴ = 1/16 in 4 half-lives. So, 30 years ÷ 4 = 7.5 years per half-life.
2. In a sample of a radioactive substance, what percentage decays in one mean lifetime?
(a) 70%
(b) 63.2%
(c) 45.8%
(d) 23%
Answer: B) 63.2%
Explanation: In one mean lifetime, approximately 63.2% of the substance decays according to the exponential decay law.
3. Which is the necessary and sufficient condition for an element to be naturally radioactive?
(a) Z > 50
(b) Z > 60
(c) Z > 70
(d) Z > 83
Answer: D) Z > 83
Explanation: All elements with atomic number greater than 83 are unstable and thus naturally radioactive.
4. During the lifetime of a radioactive element as time passes the number of its nuclei decreases and along with that_____
(a) Activity and λ go on decreasing
(b) Activity and λ go on increasing
(c) Activity decreases but λ remains constant
(d) Activity decreases but λ increases
Answer: C) Activity decreases but λ remains constant
Explanation: Decay constant (λ) is a property of the isotope and remains unchanged, while activity reduces as nuclei decay.
5. Half-life of a radioactive element is 5 min. At the end of 20 min. its _____% quantity will remain undisintegrated.
(a) 93.73
(b) 75
(c) 25
(d) 6.25
Answer: D) 6.25
Explanation: In 20 min, 4 half-lives occur: (1/2)⁴ = 1/16 = 6.25%.
6. The various series of the hydrogen spectrum, which of the following lies wholly in the ultraviolet region?
(a) Balmer Series
(b) Paschen Series
(c) Brackett Series
(d) Lyman Series
Answer: D) Lyman Series
Explanation: The Lyman series involves transitions to n=1 and lies entirely in the ultraviolet region.
7. What is the energy needed to ionize the H-atom from its second excited state if the energy of the ground state of the H-atom is 13.6 eV?
(a) 3.4 eV
(b) 1.51 eV
(c) 12.1 eV
(d) 13.6 eV
Answer: B) 1.51 eV
Explanation: Second excited state = n=3 → Energy = 13.6/9 = 1.51 eV; ionization energy from this level is 1.51 eV.
8. Which of the following is a correct statement?
(a) Equal fractions disintegrate in equal intervals of time
(b) The rate of disintegration is directly proportional to the number of atoms present
(c) A radioactive sample takes an infinite time to disintegrate completely
(d) All of the above
Answer: D) All of the above
Explanation: All statements reflect fundamental principles of radioactive decay.
9. How many spectral lines are observed when hydrogen atoms are excited from the ground state to the state of principal quantum number 4?
(a) 2
(b) 3
(c) 5
(d) 6
Answer: D) 6
Explanation: Number of lines = n(n−1)/2 = 4×3/2 = 6.
10. The quantity which is not conserved in a nuclear reaction is__________
(a) momentum
(b) charge
(c) mass
(d) none of these
Answer: C) mass
Explanation: Mass is not strictly conserved; some mass is converted into energy.
11. A radioactive nucleus emits a beta particle. The parent and daughter nuclei are________
(a) isotopes
(b) isotones
(c) isomers
(d) isobars
Answer: D) isobars
Explanation: In β-emission, atomic number changes but mass number remains the same → isobars.
12. The mass number of iron nucleus is 56. The nuclear density is____________
(a) 2.29 × 10¹⁶ kg/m³
(b) 2.29 × 10¹⁷ kg/m³
(c) 2.29 × 10¹⁷ kg/m³
(d) 2.29 × 10¹⁵ kg/m³
Answer: B) 2.29 × 10¹⁷ kg/m³
Explanation: Nuclear density is nearly constant for all nuclei and is around 2.3 × 10¹⁷ kg/m³.
13. The radius of a spherical nucleus as measured by electron scattering is 3.6 fm. What is the mass number of the nucleus most likely to be?
(a) 27
(b) 40
(c) 56
(d) 120
Answer: A) 27
Explanation: R = R₀A^(1/3), with R₀ ≈ 1.2 fm, solving 3.6 = 1.2A^(1/3) gives A ≈ 27.
14. The number of beta particles emitted by a radioactive substance is twice the number of alpha particles emitted by it. The resulting daughter is an
(a) isomer of parent
(b) isotone of parent
(c) isotope of parent
(d) isobar of parent
Answer: C) isotope of parent
Explanation: α decay lowers atomic number by 2, β⁻ increases by 1 → net change 0 in atomic number, but mass same.
15. An electron emitted in beta radiation originates from________
(a) inner orbits of an atom
(b) free electrons existing in the nuclei
(c) decay of a neutron in a nucleus
(d) photon escaping from the nucleus
Answer: C) decay of a neutron in a nucleus
Explanation: In β⁻ decay, a neutron decays into a proton, electron, and antineutrino.
16. Two elementary particles which have almost infinite life are________
(a) electron and neutron
(b) neutron and proton
(c) electron and proton
(d) none of the above
Answer: C) electron and proton
Explanation: Both are stable particles with extremely long lifetimes.
17. Out of 6C¹⁴, 7N¹³, 7N¹⁴, and 8O¹⁸, the pair of isotones is__________
(a) 6C¹⁴, 8O¹⁶
(b) 7N¹⁴, 7N¹³
(c) 7N¹⁴, 6C¹⁴
(d) 7N¹⁴, 8O¹⁶
Answer: A) 6C¹⁴, 8O¹⁶
Explanation: Isotones have the same number of neutrons; both have 8 neutrons.
18. In gamma rays emission from a nucleus,
(a) only the proton number changes
(b) both proton and neutron numbers change
(c) there is no change in proton or neutron number
(d) only the neutron number changes
Answer: C) there is no change in proton or neutron number
Explanation: Gamma emission involves energy release without changing atomic structure.
19. Which word equation represents β⁺ decay?
(a) proton → neutron + electron + electron antineutrino
(b) proton → neutron + positron + electron antineutrino
(c) proton → neutron + positron + electron antineutrino
(d) proton → neutron + positron + electron neutrino
Answer: D) proton → neutron + positron + electron neutrino
Explanation: Correct particle combination for β⁺ decay.
20. The radius of a nucleus is__________
(a) directly proportional to its mass number
(b) inversely proportional to its atomic weight
(c) directly proportional to the cube root of its mass number
(d) None of these
Answer: C) directly proportional to the cube root of its mass number
Explanation: R = R₀A^(1/3)
21. The electrons cannot exist inside the nucleus because________
(a) the de-Broglie wavelength associated with the electron in β-decay is much less than the size of the nucleus
(b) the de-Broglie wavelength associated with the electron in β-decay is much greater than the size of the nucleus
(c) the de-Broglie wavelength associated with the electron in β-decay is equal to the size of the nucleus
(d) the negative charge cannot exist in the nucleus
Answer: B) the de-Broglie wavelength associated with the electron in β-decay is much greater than the size of the nucleus
Explanation: Such a long wavelength implies the electron is not confined to the tiny nucleus.
22. When the number of nucleons in nuclei increases, the binding energy per nucleon
(a) increases continuously with mass number
(b) decreases continuously with mass number
(c) remains constant with mass number
(d) first increases and then decreases with the increase of mass number
Answer: D) first increases and then decreases with the increase of mass number
Explanation: BE/nucleon peaks around Fe and drops for heavier elements.
23. The radius of a spherical nucleus as measured by electron scattering is 3.6 fm. What is the mass number of the nucleus most likely to be?
(a) 27
(b) 40
(c) 56
(d) 120
Answer: A) 27
Explanation: As earlier, R = R₀A^(1/3) → A ≈ 27.
24. During negative β-decay, an antineutrino is also emitted along with the emitted electron. Then,
(a) only linear momentum will be conserved
(b) total linear momentum and angular momentum but not energy will be conserved
(c) total linear momentum, and energy but not angular momentum will be conserved
(d) total linear momentum, angular momentum, and energy will be conserved
Answer: D) total linear momentum, angular momentum, and energy will be conserved
Explanation: All conservation laws hold true in nuclear reactions.
25. In nuclear reaction, there is conservation of_________
(a) mass only
(b) energy only
(c) momentum only
(d) mass, energy, and momentum
Answer: D) mass, energy, and momentum
Explanation: All three are conserved according to Einstein’s mass-energy equivalence and Newtonian mechanics.