JEE Main 2025 Apr 7 Shift 2, Chemistry Q6: Periodicity In Atomic Properties

JEE Main2025Apr 7, Shift 2Chemistry

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

A
r $_{B r}$ < r $_{K}$
B
r $_{M g}$ < r $_{A l}$
C
r $_{R b}$ < r $_{C s}$
D
r $_{A t}$ < r $_{C s}$

Solution

Moving down a group, atomic radius increases because a new shell is added, so r $_{R b}$ < r $_{C s}$ and r $_{A t}$ < r $_{C s}$ are both valid trends.

Comparing Br (period 4, group 17) with K (period 4, group 1): across a period, radius decreases left to right, and K is far to the left of Br, so r $_{B r}$ < r $_{K}$ is also a correct trend.

Across period 3, atomic radius generally decreases from left to right due to increasing effective nuclear charge, so Mg (group 2) should have a larger radius than Al (group 13), i.e. r $_{M g}$ > r $_{A l}$ . The statement r $_{M g}$ < r $_{A l}$ therefore reverses the correct trend.

$∴$ Option (2) is the incorrect trend.

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JEE Main 2025 Apr 7 Shift 2, Chemistry Q6: Periodicity In Atomic Properties

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