NEET PhysicsUpdated 19 Oct 2026

Nuclei: NEET PYQs and weightage

Nuclei carries 2.9 of 100 Physics marks in NEET by past-paper share: 22 of the 758 tagged NEET Physics PYQs in the ViJEEta bank (NEET 2013–2026). It ranks 18 of 30 Physics chapters.

Take the 25-question Nuclei test Formula sheet ↓All NEET Physics chapters

2.9/100 Weight in Physics

Exam importance (3/5, by past-paper share)

22 NEET PYQs

168 Practice questions

157 With measured difficulty

How the weight is computed: this chapter's tagged NEET PYQs divided by all tagged NEET Physics PYQs in the bank (22 of 758), times 100, with repeated questions counted once. The bank does not store the year of each NEET question, so none is printed. Computed from the bank at build time. Updated 19 Oct 2026.

Nuclei: formula sheet for NEET

14 formulas, each with when to use it. Copy it onto one page of your notebook: that page is this chapter's handbook.

Mass defect
$Δ M = [Z m_{p} + (A - Z) m_{n}] - M$
Use it when: you need how much lighter a nucleus is than its separate protons and neutrons
Binding energy
$E_{b} = Δ M c^{2}$
Use it when: you need the energy to pull a nucleus fully apart into its nucleons
Mass to energy shortcut
$1 u = 931.5 MeV / c^{2}$
$E_{b} (MeV) = Δ M (in u) \times 931.5$
Use it when: the masses are given in u and the answer is wanted in MeV
Binding energy per nucleon
$E_{bn} = \frac{E _{b}}{A}$
Use it when: comparing stability. Higher $E_{bn}$ means more tightly bound. It is about $8 MeV$ for $30 < A < 170$ , peaks near $8.75 MeV$ at $A = 56$ , and is about $7.6 MeV$ at $A = 238$
Q-value
$Q = (\sum m_{initial} - \sum m_{final}) c^{2} = K_{final} - K_{initial}$
Use it when: deciding whether a reaction or decay releases energy. $Q > 0$ is exothermic and $Q < 0$ is endothermic
Nuclear radius
$R = R_{0} A^{1/3} (with R_{0} = 1.2 fm, 1 fm = 1 0^{- 15} m)$
Use it when: finding the size of a nucleus from its mass number
Radius ratio
$\frac{R _{1}}{R _{2}} = (\frac{A _{1}}{A _{2}})^{1/3}$
Use it when: comparing the sizes of two nuclei, for example Au-197 and Ag-107
Nuclear density
$ρ = \frac{A m _{u}}{\frac{4}{3} π R _{0}^{3} A} = \frac{m _{u}}{\frac{4}{3} π R _{0}^{3}} \approx 2.3 \times 1 0^{17} kg/m^{3}$
Use it when: asked how density depends on $A$ . $A$ cancels, so the density is the same for every nucleus
Composition
$A = Z + N$
Use it when: counting neutrons, or balancing a reaction. Total $Z$ and total $A$ must match on both sides
Mass-energy
$E = m c^{2}$
Use it when: converting any mass to energy. $1 g$ gives $9 \times 1 0^{13} J$
Fission energy estimate
$Q \approx A \times (gain in E_{bn})$
$240 \times 0.9 MeV \approx 216 MeV \approx 200 MeV per fission$
Use it when: estimating fission energy from the binding energy curve
Coulomb barrier
$U = \frac{1}{4 π ε _{0}} \frac{q _{1} q _{2}}{r _{1} + r _{2}}$
Use it when: finding the energy two nuclei need to just touch. Use the sum of the radii as the separation, not one radius
Fusion temperature
$\frac{3}{2} k T = K$
$K \approx 400 keV (two protons) \Rightarrow T \sim 3 \times 1 0^{9} K$
Use it when: estimating the temperature at which average particles can cross the Coulomb barrier
Average atomic mass
$m_{avg} = \sum (fractional abundance \times isotope mass)$
Use it when: isotope masses and percentages are given. Chlorine works out to $35.47 u$

Trap

Mixing atomic and nuclear masses. Tables give atomic masses, which include the electrons. With atomic masses, use m_H = 1.007825 u in place of m_p so the electrons cancel. Never put m_p next to an atomic mass of the nucleus.

How does NEET ask Nuclei?

8 real previous-year questions from this chapter, as printed in the paper, each with its worked solution. Answer the first one here with no sign-in.

Q1PhysicsNEET UG PYQMass-Energy and Nuclear Binding Energy

Try right here · No sign-in

Consider the following nuclear reaction

^{238} U ⟶^{234} Th +^{4} He

Take masses of

^{238} U,^{234} Th

and

^{4} He

238.050 u, 234.043 u

and 4.003 u , respectively. The

Q

value for the reaction, in keV , is: [Given:

1 u = 931.5 MeV c^{- 2}

]

Answer key (D) & worked solution

Correct answer: Option D

Q

-value for the nuclear reaction is given by,

Q = Δ m c^{2}

^{238} U ⟶^{234} Th +^{4} He

has mass defect

Δ m = m_{reactants} - m_{products}

\Rightarrow Δ m = 238.050 - (234.043 + 4.003) = 0.004 u

∴ Q = 0.004 \times 931.5 MeV = 3.726 MeV = 3726 keV

Q2PhysicsNEET UG PYQRadioactivity*

A radio isotope ‘X’ with a half life 1.4 × 10

^{9}

years decays to ‘Y’ which is stable. A sample of the rock from a cave was found to contain ‘X’ and ‘Y’ in the ratio 1 : 7. The age of the rock is:

A4.20 × 10

^{9}

years

B8.40 × 10

^{9}

years

C1.96 × 10

^{9}

years

D3.92 × 10

^{9}

years

Answer key (A) & worked solution

Correct answer: Option A

N_{x} : N_{y} = 1 : 7

N_{0} = 8 x

N_{x} = x & N_{y} = y

N_{x} = N_{0} 2^{- \frac{t}{T _{1/2}}}

x = (8 x) 2^{- \frac{t}{T _{1/2}}}

\Rightarrow \frac{t}{T _{1/2}} = 3

t = 3 \times 1.4 \times 1 0^{9} = 4.2 \times 1 0^{9}

years

Q3PhysicsNEET UG PYQRadioactivity*

For a radioactive material, half-life is 10 minutes. If initially there are 600 number of nuclei, the time taken (in minutes) for the disintegration of 450 nuclei is

A30

B10

C20

D15

Answer key (C) & worked solution

Correct answer: Option C

Number of nuclei remaining = 600 - 450 = 150

\frac{N}{N _{0}} = (\frac{1}{2})^{n}

\frac{150}{600} = (\frac{1}{2})^{\frac{t}{t _{1/2}}}

(\frac{1}{2})^{2} = (\frac{1}{2})^{\frac{t}{t _{1/2}}}

t = 2 t_{1/2} = 2 \times 10

= 20 minutes

Q4PhysicsNEET UG PYQNuclear Energy

When a uranium isotope

_{92}^{235} U

is bombarded with a neutron, it generates

_{36}^{89} K r,

three neutrons and:

_{36}^{101} K r

_{36}^{103} K r

_{56}^{144} B a

_{40}^{91} Z r

Answer key (C) & worked solution

Correct answer: Option C

_{92}^{235} U +_{0} n^{1} \to_{36}^{89} K_{r} +_{Z}^{A} Y + 3_{0} n^{1}

92 = 36 + Z

Z = 56

A + 89 + 3 = 235 + 1 \Rightarrow A = 144

Q5PhysicsNEET UG PYQSize of the Nucleus

If radius of the

_{13}^{27} A l

nucleus is taken to be

R_{A l}

, then the radius of

_{53}^{125}

Te nucleus is nearly:

(\frac{13}{53})^{1/3} R_{A l}

(\frac{53}{13})^{1/3} R_{A l}

\frac{5}{3} R_{A l}

\frac{3}{5} R_{A l}

Answer key (C) & worked solution

Correct answer: Option C

Radius of the nucleus goes as R ∝ A 1 / 3 , where A is the atomic mass. If R

_{T e}

is the radius of the nucleus of tellurium atom and R

_{A l}

is the radius of the nucleus of aluminum atom we have

\frac{R _{T e}}{R _{A l}} = \frac{( 125 ) ^{1/3}}{( 27 ) ^{1/3}} = \frac{5}{3} ∴ R_{T e} = \frac{5}{3} R_{A l}

Q6PhysicsNEET UG PYQMass-Energy and Nuclear Binding Energy

The energy equivalent of 0.5 g of a substance is :

1.5 \times 1 0^{13} J

0.5 \times 1 0^{13} J

4.5 \times 1 0^{16} J

4.5 \times 1 0^{13} J

Answer key (D) & worked solution

Correct answer: Option D

E = Δ m c^{2} = 0.5 \times 1 0^{- 3} \times (3 \times 1 0^{8})^{2}

= 0.5 \times 1 0^{- 3} \times 9 \times 1 0^{16}

E = 4.5 \times 1 0^{13} J

Q7PhysicsNEET UG PYQSize of the Nucleus

An unknown nucleus has a nuclear density of

2.29 \times 1 0^{17} kg / m^{3}

and mass of

19.926 \times 1 0^{- 27} kg

. Its mass number

A

is approximately: (Take

R_{0} = 1.2 \times 1 0^{- 15} m, 4 π = 12.56

)

A12

B19

C20

D16

Answer key (A) & worked solution

Correct answer: Option A

Given

ρ = 2.29 \times 1 0^{17} kg / m^{3}

, mass

m = 19.926 \times 1 0^{- 27} kg

R_{0} = 1.2 \times 1 0^{- 15} m

and

R = R_{0} A^{\frac{1}{3}}

Now use volume

= \frac{Mass}{Density}

\Rightarrow \frac{4}{3} π R^{3} = \frac{M}{ρ}

\Rightarrow \frac{4}{3} π [R_{0} (A)^{1/3}]^{3} = \frac{M}{ρ}

\Rightarrow \frac{4}{3} π R_{0}^{3} A = \frac{M}{ρ}

\Rightarrow A = \frac{M}{ρ} \times \frac{3}{4 π \times R _{0}^{3}} = \frac{19.926 \times 1 0 ^{- 27} \times 3}{2.29 \times 1 0 ^{17} \times 12.56 \times ( 1.2 \times 1 0 ^{- 15} ) ^{3}} \approx 12

Q8PhysicsNEET UG PYQRadioactivity*

A half-life of a radioactive nuclide is 100 hours. The fraction of original activity that will remain after 150 hours would be:

\frac{2}{3}

\frac{2}{3 2}

\frac{1}{2}

\frac{1}{2 2}

Answer key (D) & worked solution

Correct answer: Option D

N = N_{0} (\frac{1}{2})^{n}

= N_{0} (\frac{1}{2})^{\frac{150}{100}}

= N_{0} (\frac{1}{2})^{3/2}

\frac{N}{N _{0}} = \frac{1}{2 2}

Which topics in Nuclei carry the most questions?

All 7 topics, by tagged PYQs, then practice questions. Counted from the bank. Updated 19 Oct 2026.

Topic	PYQs	Practice questions
Radioactivity*	9	64
Mass-Energy and Nuclear Binding Energy	6	45
Size of the Nucleus	3	22
Atomic Masses and Composition of Nucleus	2	8
Nuclear Energy	1	22
Miscellaneous Examples	1	2
Nuclear Force	0	5

Why does Nuclei show "–" until you answer 3 questions?

Unknown is not zero. Until you answer at least 3 graded questions in Nuclei, ViJEEta shows – instead of a zero or a 50% default. Book exercises can raise chapter mastery up to 0.60, adaptive practice up to 0.75, and only a timed chapter test or mock can certify 0.80 and above.

How ViJEEta scores you

What happens when you test Nuclei?

Every chapter test is 25 questions. It starts at moderate difficulty and adapts after each saved answer. If you open a solution before answering, that attempt earns no credit, so your mastery stays honest.

Start the Nuclei test

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Nuclei: NEET PYQs and weightage

Nuclei: formula sheet for NEET

Mass defect

Binding energy

Mass to energy shortcut

Binding energy per nucleon

Q-value

Nuclear radius

Radius ratio

Nuclear density

Composition

Mass-energy

Fission energy estimate

Coulomb barrier

Fusion temperature

Average atomic mass

How does NEET ask Nuclei?

Which topics in Nuclei carry the most questions?

Why does Nuclei show "–" until you answer 3 questions?

What happens when you test Nuclei?

Chapters either side of Nuclei by weight