With the Class 12 Physics Board Exam scheduled for February 21, 2026, students must now prioritize high-weightage and numerically scoring chapters like Nuclei. This chapter is compact but extremely important, often contributing direct formula-based numericals and reasoning-based theory questions.
Practicing Nuclei class 12 Important Questions in the final revision phase can help secure easy marks because most questions revolve around fixed formulas such as mass defect, binding energy, and radioactive decay law.
Regular practice of Nuclei class 12 Question Answers along with properly structured Nuclei 12 solutions ensures you understand step marking and unit handling.
Nuclei Class 12 Important Questions
This chapter primarily revolves around numerical accuracy and conceptual clarity. The most important areas from which questions are repeatedly asked include Mass defect, binding energy and binding energy per nucleon, nuclear stability, radioactive decay law, half-life and mean life, and nuclear fission and nuclear fusion.
Below are the Nuclei Class 12 MCQ as well as important questions along with answers:
1. Elements having different atomic number as well as different mass number, but same number of neutrons, are known as [OD 2007]
(A) isobars
(B) isotones
(C) isotopes
(D) isodiapheres
1. (B)
Sol. The elements having different atomic number as well as different mass number, but same number of neutrons, are known as isotones. Thus (B) is correct option.
2. If M is the atomic mass and A is the mass number, then the packing fraction is given by [SQP 2010]
2. (B)
Sol. Atomic mass = M and
Mass number = A
Packing fraction is the ratio of atomic mass M minus mass number A to the mass number A
3. An element has binding energy 8 eV per nucleon. If it has total binding energy of 128 eV, then the number of nucleons are [Delhi 2011]
(A) 8
(B) 16
(C) 32
(D) 64
4. How is the radius of a nucleus related to its mass number? [OD 2011]
6. A chain reaction dies out sometimes. Why? [OD 2003]
Sol. A chain reaction may die out due to any of the following causes:
1. Excessive neutron leakage if the size of the fissionable material is smaller than the critical size.
2. Fast neutrons may escape the fissionable material without causing further fissions.
3. Some neutrons may suffer non–fission capture by 
7. Calculate the energy released/absorbed (in MeV) in the nuclear reaction:
9. (i) What characteristic property of nuclear force explains the constancy of binding energy per nucleon (BE/A) in the range of mass number.
'A' .... lying 30 < A < 170?
(ii) Show that the density of nucleus over a wide range of nuclei is constant independent of mass number A. [OD 2012, SQP 2015]
Sol. (i) Saturation or short range nature of nuclear forces.
(ii) The radius (size) R of nuclear is related to its mass number (A) as
If m is the average mass of a nucleon, then mass of nucleus = mA, Where A is mass number.
How to Revise Nuclei Class 12 Question Answers in the Final Week
As the February 21 exam approaches, follow this focused strategy:
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Prepare a one-page formula sheet (binding energy, decay law, half-life relation).
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Solve at least 8–10 numericals from Nuclei 12 Solutions.
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Practice previous year board questions.
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Revise definitions like nuclear force, isotopes, isobars, and isotones.
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Attempt mixed sets including Nuclei Class 12 MCQ.
Consistent revision of Nuclei Class 12 Important Questions can easily help secure 5–8 marks from this chapter.