NucleiNEET MCQs with solutions
Nuclei covers nuclear structure, mass defect, binding energy, radioactivity (α, β, γ decay), half-life, nuclear fission and fusion. NEET tests mass defect and binding energy calculations, radioactive decay law, half-life problems and the difference between fission and fusion.
- Class
- 12 Physics
- Free on this page
- 24 questions
- In the RankUp app
- 502 questions
- ELITE questions
- 188
- NCERT topics
- 12
Practise 24 questions
Tap an option to check it. Questions from every NCERT topic in this chapter, from easy to hard.
Q1Mixed Revision
A radioactive material has a half-life of 10 minutes. Initially there are 600 nuclei. The time required for 450 nuclei to disintegrate is
Not quite — the answer is C.
Remaining = 600 − 450 = 150. Fraction left = 150/600 = 1/4 = (1/2)². Two half-lives elapsed, so t = 2 × 10 = 20 min. Option D (30 min) is the trap for students who calculate half of 450 instead of working with remaining nuclei.
Q2Mixed Revision
A radioactive sample X has half-life 1.4×10⁹ years and decays to stable Y. If a rock contains X and Y in the ratio 1:7, its approximate age is
Not quite — the answer is B.
Original amount = X + Y = 8 parts. Remaining fraction = 1/8 = (1/2)³, so three half-lives elapsed. Age = 3 × 1.4×10⁹ = 4.2×10⁹ years. Common trap: using ratio 1:7 directly as 7 half-lives instead of finding original total.
Q3Grand Test
For a nuclear fusion process, the suitable nuclei are
Not quite — the answer is B.
Fusion releases energy when light nuclei combine to form a heavier nucleus with higher binding energy per nucleon. Heavy nuclei like uranium undergo fission, not fusion, to release energy.
Q4Grand Test
A nuclear reactor uses water as a coolant primarily because of its
Not quite — the answer is D.
A coolant must absorb large amounts of heat with minimal temperature rise. Water's high specific heat capacity satisfies this. Low specific heat (Option C) would be the worst property for a coolant.
Q5Atomic Mass, Mass Defect and Binding Energy
If M(A,Z) is the nuclear mass, Mp and Mn are proton and neutron masses, the correct expression for binding energy BE is
Not quite — the answer is A.
Mass defect Δm = ZMp + (A-Z)Mn - M(A,Z) is positive for all bound nuclei; BE = Δmc². Option B inverts the sign giving a negative BE. Options C and D add nuclear mass instead of subtracting, giving a physically meaningless result.
Q6Atomic Mass, Mass Defect and Binding Energy
The mass defect of a nucleus is 0.042 u. Taking 1 u = 931.5 MeV/c², its total binding energy is approximately
Not quite — the answer is D.
BE = Δm × 931.5 = 0.042 × 931.5 = 39.123 MeV, approximately 39.1 MeV. Option A arises from dividing 931.5 by 0.042 — inverting the multiplication. Option C is the trap of multiplying 0.042 by 1000 instead of 931.5.
Q7Binding Energy Curve
According to the binding energy per nucleon curve, which region contains the most tightly bound nuclei?
Not quite — the answer is C.
The BE/nucleon curve reaches its maximum of approximately 8.75 MeV near A = 56 (the iron region). Nuclei here are most tightly bound per nucleon and hence most stable. Both very light and very heavy nuclei lie on the lower sides of the curve. Option D is a common misconception.
Q8Binding Energy Curve
Which of the following correctly explains why a very heavy nucleus can release energy by undergoing fission into intermediate-mass nuclei?
Not quite — the answer is A.
Heavy nuclei lie on the descending side of the BE/nucleon curve and have lower BE/nucleon than intermediate-mass nuclei. Fission products lie closer to the A = 56 peak. Their higher BE/nucleon means greater total BE, and the difference is released as energy. Option D describes the opposite of what the curve shows.
Q9Radioactive Decay Law
The number of undecayed radioactive nuclei at time t is given by
Not quite — the answer is C.
The decay law is N = N0 e^(-λt) where the negative exponent models continuous decrease. Option A shows growth; B is a linear approximation; C wrongly places λ in the denominator making the exponent dimensionally inconsistent.
Q10Radioactive Decay Law
A radioactive sample initially contains 8000 nuclei. After one half-life, the number of undecayed nuclei is
Not quite — the answer is B.
After one half-life exactly half the nuclei remain: N = N0/2 = 8000/2 = 4000. Option A corresponds to two half-lives, option D to three half-lives, and option C represents only 25% decay which does not correspond to any whole half-life.
Q11Nuclear Fusion
Nuclear fusion of suitable light nuclei releases energy. Which of the following correctly explains this?
Not quite — the answer is C.
As light nuclei fuse, the product moves toward the higher-BE/nucleon region of the curve. The increase in total binding energy equals energy released. Only the mass defect — not total mass — converts to energy. Option D misattributes the role of the Coulomb force.
Q12Nuclear Fusion
Nuclear fusion requires extremely high temperature. Which of the following correctly explains this?
Not quite — the answer is A.
Light nuclei are positively charged and strongly repel each other. Very high temperature provides the thermal kinetic energy needed to bring nuclei within ~10⁻¹⁵ m where the nuclear force takes over. Options B, C and D each misidentify what temperature achieves physically.
478 more questions on this chapter are waiting in the app
Every one with a detailed explanation, plus flashcards and chapter tests.
Get RankUp on Google PlayQ13Nuclear Fission
Nuclear fission is best explained by which model of the nucleus?
Not quite — the answer is A.
The liquid-drop model treats the nucleus as incompressible nuclear fluid and explains collective deformation leading to fission. Yukawa theory addresses nuclear force; the independent-particle model explains magic numbers, not fission.
Q14Nuclear Fission
Energy is released in nuclear fission because
Not quite — the answer is A.
Fission products have higher total binding energy than the parent; the difference appears as kinetic energy of fragments and radiation. Option B is the opposite of what occurs. Option D reverses the mass-energy process.
Q15Nuclear Energy and Applications
Water is used as a coolant in a nuclear reactor mainly because of its
Not quite — the answer is B.
High specific heat means water absorbs large heat per degree rise, making it effective at removing reactor heat. Low boiling point would be a disadvantage in high-temperature operation. Thermal expansion is irrelevant to coolant function.
Q16Nuclear Energy and Applications
Solar energy is mainly produced by
Not quite — the answer is C.
The Sun generates energy via nuclear fusion of hydrogen into helium, releasing energy due to mass defect and increased binding energy per nucleon. Fission involves heavy nuclei; combustion is a chemical process — neither applies to the Sun.
Q17Nuclear Size and Density
If the nuclear radius of ^27_13Al is 3.6 fm, the approximate nuclear radius of ^125_52Te is
Not quite — the answer is D.
R ratio = (A2/A1)^(1/3) = (125/27)^(1/3) = 5/3. So R2 = 3.6 × 5/3 = 6.0 fm. Option A (4.8 fm) arises from using ratio 4/3 by confusing cube-root of 64 with 125. The ratio 125/27 = (5/3)^3, so the cube root is exactly 5/3.
Q18Nuclear Size and Density
Two nuclei have mass numbers in the ratio 1:3. The ratio of their nuclear densities is
Not quite — the answer is A.
Nuclear density rho = M/V; M proportional to A and V proportional to A, so rho is independent of A. The ratio is 1:1 for any two nuclei regardless of their mass numbers. Option B (1:3) is the trap for students who incorrectly assume density scales with A.
Q19Discovery and Composition of Nucleus
The mass number A of a nucleus is always
Not quite — the answer is D.
A = Z + N and N is always ≥ 0, so A ≥ Z always. A equals Z only for hydrogen-1 (N=0); for all heavier nuclei A > Z. Options A and C are impossible since A can never be less than Z.
Q20Discovery and Composition of Nucleus
The nuclei of which pair have the same number of neutrons (isotones)?
Not quite — the answer is A.
N(Se)=74-34=40; N(Ga)=71-31=40 — isotones confirmed. Option B: Sr-84 N=46, Sr-86 N=48 — isotopes. Option C: Mo-92 N=50, Zr-92 N=52 — isobars. Option D: Ca-40 N=20, S-32 N=16 — neither.
Q21Radioactivity
An alpha particle consists of
Not quite — the answer is A.
An alpha particle is the nucleus of helium-4 with 2 protons and 2 neutrons and no electrons. Options B and C wrongly include electrons, which are not nuclear constituents.
Q22Radioactivity
The penetrating power of alpha, beta and gamma radiations in increasing order is
Not quite — the answer is B.
Penetrating power increases as alpha < beta < gamma. The classic trap is reversing this with ionising power order, which is the opposite: alpha > beta > gamma.
Q23Half-life and Mean Life
A radioactive sample has a half-life of 30 days. The time required for three-fourths of the initial nuclei to decay is
Not quite — the answer is B.
Three-fourths decayed means one-fourth remains. Since 1/4 = (1/2)², exactly 2 half-lives have elapsed. Time = 2 × 30 = 60 days. Option C (90 days) is the trap — students count three-fourths decayed as three half-lives rather than converting to fraction remaining first.
Q24Half-life and Mean Life
A radioactive substance has a half-life of 10 years. Its mean life is approximately
Not quite — the answer is D.
τ = T½/ln2 = T½/0.693 = 10/0.693 ≈ 14.43 years. Option A (6.93) inverts the relationship giving 0.693 × T½; option B confuses mean life with half-life; option C uses an incorrect conversion factor of approximately 1.23.
ELITE question · AIR under 50 level
This chapter has 188 ELITE questions for students aiming at the very top. They are only in the app.
Unlock ELITE questions in the appKey Nuclear Concepts
Quick revision: most questions in this chapter test these facts.
| Concept | Key Formula / Fact |
|---|---|
| Mass defect | Δm = [Zm_p + (A−Z)m_n] − M_nucleus; converted to energy via E = Δmc² |
| Binding energy | BE = Δm × 931.5 MeV; BE/A peaks at Fe (most stable) |
| Radioactive decay | N = N₀e^(−λt); λ = 0.693/t½; activity A = λN |
| Half-life | t½ = 0.693/λ; after n half-lives: N = N₀/2ⁿ |
| Alpha decay | A→A−4, Z→Z−2; emits ⁴He nucleus |
| Fission vs Fusion | Fission: heavy → light (U-235); Fusion: light → heavy (H→He in stars); both release energy |
What the app covers in this chapter
502 questions in total, each with a detailed explanation.
| Mixed Revision | 99 |
| Grand Test | 78 |
| Atomic Mass, Mass Defect and Binding Energy | 40 |
| Binding Energy Curve | 40 |
| Radioactive Decay Law | 40 |
| Nuclear Fusion | 40 |
| Nuclear Fission | 38 |
| Nuclear Energy and Applications | 37 |
| Nuclear Size and Density | 26 |
| Discovery and Composition of Nucleus | 24 |
| Radioactivity | 20 |
| Half-life and Mean Life | 20 |
Questions students ask
Is Nuclei important for NEET?
Yes — mass defect, binding energy, radioactive decay law and half-life problems are tested regularly. Both conceptual and numerical questions appear.
Which topics should I revise first?
Focus on mass defect and binding energy per nucleon, radioactive decay law with half-life, α/β/γ decay equations and changes in A and Z, and the energy released in fission vs fusion.
How many questions from this chapter are on RankUp?
The RankUp app has 502 questions on Nuclei, including 188 ELITE questions. Every question has a detailed explanation.
