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

Asked in JEE Main 23rd Jan 2nd Shift 2026 · Composition, isotopes and isobars

(1) ²₁H and ³₁H
(2) ²³⁶₉₂U and ²³⁸₉₂U
(3) ³₁H and ³₂He
(4) ¹⁹⁸₈₀Hg and ¹⁹⁷₇₉Au

Answer: (3) ³₁H and ³₂He

Step-by-step solution

Isobars have the same mass number A.

³₁H and ³₂He both have A=3.

Why the other options are wrong

(1) These are isotopes (same Z).
(2) These are isotopes.
(4) Different A; these are isotones (same N=118).

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