JEE Main 2026 — Physics Modern Physics

2026mcqeasy

Which of the following pair of nuclei are isobars of the element?

Official previous-year question

Held on 23 Jan 2026 · Verified 6 Jul 2026.

Options

A
${ }_{1}^{3} \mathrm{H}$ and ${ }_{2}^{3} \mathrm{He}$
B
${ }_{1}^{2} \mathrm{H}$ and ${ }_{1}^{3} \mathrm{H}$
C
${ }_{80}^{198} \mathrm{Hg}$ and ${ }_{79}^{197} \mathrm{Au}$
D
${ }_{92}^{236} \mathrm{U}$ and ${ }_{92}^{238} \mathrm{U}$

Did you get this right?

Solution

Isobars are atoms of different chemical elements that have the same number of nucleons (mass number $A$ ), but different atomic numbers ( $Z$ ).

In the given options:

(1) $_1^3\text{H}$ and $_2^3\text{He}$ : Both have the same mass number $A = 3$ . Since they have different atomic numbers ( $Z=1$ and $Z=2$ ), they are isobars.

(2) $_1^2\text{H}$ and $_1^3\text{H}$ : These have the same atomic number ( $Z=1$ ) but different mass numbers. They are isotopes.

(3) $_{80}^{198}\text{Hg}$ and $_{79}^{197}\text{Au}$ : These have different mass numbers ( $198$ and $197$ ).

(4) $_{92}^{236}\text{U}$ and $_{92}^{238}\text{U}$ : These have the same atomic number ( $Z=92$ ) but different mass numbers. They are isotopes.

Thus, the pair $_1^3\text{H}$ and $_2^3\text{He}$ are isobars.

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JEE Main 2026 — Physics Modern Physics

2026mcqeasy

Which of the following pair of nuclei are isobars of the element?

Official previous-year question

Held on 23 Jan 2026 · Verified 6 Jul 2026.

Options

A
${ }_{1}^{3} \mathrm{H}$ and ${ }_{2}^{3} \mathrm{He}$
B
${ }_{1}^{2} \mathrm{H}$ and ${ }_{1}^{3} \mathrm{H}$
C
${ }_{80}^{198} \mathrm{Hg}$ and ${ }_{79}^{197} \mathrm{Au}$
D
${ }_{92}^{236} \mathrm{U}$ and ${ }_{92}^{238} \mathrm{U}$

Did you get this right?

Solution

Isobars are atoms of different chemical elements that have the same number of nucleons (mass number $A$ ), but different atomic numbers ( $Z$ ).

In the given options:

(1) $_1^3\text{H}$ and $_2^3\text{He}$ : Both have the same mass number $A = 3$ . Since they have different atomic numbers ( $Z=1$ and $Z=2$ ), they are isobars.

(2) $_1^2\text{H}$ and $_1^3\text{H}$ : These have the same atomic number ( $Z=1$ ) but different mass numbers. They are isotopes.

(3) $_{80}^{198}\text{Hg}$ and $_{79}^{197}\text{Au}$ : These have different mass numbers ( $198$ and $197$ ).

(4) $_{92}^{236}\text{U}$ and $_{92}^{238}\text{U}$ : These have the same atomic number ( $Z=92$ ) but different mass numbers. They are isotopes.

Thus, the pair $_1^3\text{H}$ and $_2^3\text{He}$ are isobars.

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JEE Main 2026 — Physics Modern Physics

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JEE Main 2026 — Physics Modern Physics

Options

Did you get this right?

Solution

Your note

JEE Main Modern Physics in other years

More JEE Main Modern Physics questions

Other Physics topics for JEE Main

Mechanics

Electromagnetism

Optics

Thermodynamics

Waves & Oscillations

Keep practicing Modern Physics