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

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Which one of the following alkaline earth metal ions has the highest ionic mobility in its aqueous solution?

(A) $Be^{2 +}$
(B) $Mg^{2 +}$
(C) $Ca^{2 +}$
(D) $Sr^{2 +}$ ✓ Correct

Answer: (D)

Solution

Ionic mobility in aqueous solution depends on two factors:

Size of the gaseous ion (larger ions have higher mobility)
Extent of hydration (less hydration means higher mobility)

Among alkaline earth metal ions, as we move down the group from Be²⁺ to Sr²⁺:

Ionic size increases: Be²⁺ < Mg²⁺ < Ca²⁺ < Sr²⁺
Charge density decreases
Extent of hydration decreases

Sr²⁺ has the largest ionic size and lowest extent of hydration among the given options, resulting in the highest ionic mobility in aqueous solution.

The answer is

Sr^{2 +}

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

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

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