JEE Main · 2022 · 25 Jul 2022 · Shift 1 · s-Block Elements

Choose the correct order of density of the alkali metals :

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

Answer: (A)

Solution

The density order of alkali metals is anomalous. Li has the lowest density, followed by K (which is less dense than Na due to larger atomic size with less proportional mass increase). The order is: Li < K < Na < Rb < Cs. This is a factual trend in Group 1 elements.

JEE Main · 2022 · 25 Jul 2022 · Shift 1 · Single correct option

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