JEE Main · 2021 · 22 Jul 2021 · Shift 2 · p-Block Elements

Which one of the following group - 15 hydride is the strongest reducing agent?

(A) $AsH_{3}$
(B) $SbH_{3}$
(C) $BiH_{3}$ ✓ Correct
(D) $PH_{3}$

Answer: (C)

Solution

The reducing power of a group-15 hydride depends on how easily the

E - H

bond is broken to release hydrogen. Going down the group the central atom grows larger and its orbital overlaps less effectively with the small hydrogen orbital, so the bond dissociation enthalpy falls steadily from

N H_{3}

Bi H_{3}

. The bismuth-hydrogen bond is the weakest of the set, so

Bi H_{3}

gives up hydrogen most readily and is the strongest reducing agent.

JEE Main · 2021 · 22 Jul 2021 · Shift 2 · Single correct option

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