JEE Main 2026 Jan 23 Shift 2, Physics Q12: Radioactivity

JEE Main2026Jan 23, Shift 2Physics

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

Solution

Isobars are nuclei with the same mass number ( $A$ ) but different atomic numbers ( $Z$ ).

(1) $_{1}^{2} H$ and $_{1}^{3} H$ : same $Z$ , different $A$ . These are isotopes.

(2) $_{92}^{236} U$ and $_{92}^{238} U$ : same $Z$ , different $A$ . Isotopes.

(3) $_{80}^{198} H g$ and $_{79}^{197} A u$ : different $A$ and different $Z$ . Neither isotopes nor isobars.

(4) $_{1}^{3} H$ and $_{2}^{3} H e$ : same $A = 3$ , different $Z$ (1 vs 2). Isobars.

Concept behind this question

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