JEE Main · 2026 · 23 Jan 2026 · Shift 2 · Modern Physics

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

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

Answer: (D)

Solution

Isobars are nuclei with the same mass number

A

but different atomic numbers

Z

. Among the pairs,

_{1}^{2} H

and

_{1}^{3} H

Z

(isotopes);

_{92}^{236} U

and

_{92}^{238} U

Z

(isotopes);

_{80}^{198} Hg

and

_{79}^{197} Au

differ in both

A

and

Z

. Only

_{1}^{3} H

and

_{2}^{3} He

have the same mass number

A = 3

with different atomic numbers, so these two are isobars.

JEE Main · 2026 · 23 Jan 2026 · Shift 2 · Single correct option

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