JEE Main · 2023 · 12 Apr 2023 · Shift 1 · s-Block Elements

The density of alkali metals is in the order

(A)Na < K < Cs < Rb
(B)K < Na < Rb < Cs✓ Correct
(C)K < Cs < Na < Rb
(D)Na < Rb < K < Cs

Answer: (B)

Solution

In general, moving down Group 1, both mass and volume increase, but mass increases more prominently, so density increases. However, potassium (K) is an exception. Due to the presence of empty 3d subshells, the increase in atomic size for K is more prominent compared to the increase in mass, making K less dense than Na. After K, the trend resumes with increasing density. Therefore, the correct order is: K < Na < Rb < Cs.

JEE Main · 2023 · 12 Apr 2023 · Shift 1 · Single correct option

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