JEE Main · 2025 · 07 Apr 2025 · Shift 2 · Classification of Elements and Periodicity

Choose the incorrect trend in the atomic radii (r) of the elements :

(A) $r_{Br} < r_{K}$
(B) $r_{Mg} < r_{Al}$ ✓ Correct
(C) $r_{R b} < r_{C s}$
(D) $r_{A t} < r_{C s}$

Answer: (B)

Solution

Across a period the atomic radius shrinks as the nuclear charge grows, and down a group it expands as fresh shells are added. Potassium lies at the left of its period and is much larger than bromine at the right, so bromine being smaller than potassium is a sound trend. Caesium sits below rubidium and is larger, and caesium, far to the left, is larger than astatine, both sound. Magnesium and aluminium are neighbours in the same period with magnesium to the left, so magnesium is the larger of the two; the claim that magnesium is smaller than aluminium reverses this and is the incorrect trend.

JEE Main · 2025 · 07 Apr 2025 · Shift 2 · Single correct option

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JEE Main · 2025 · 07 Apr 2025 · Shift 2 · Classification of Elements and Periodicity

Solution

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