What is the increasing order of volatility of the following hydrides?
`PH_(3),NH_(3),AsH_(3)` , and `SbH_(3)`.

Explanation

(a)`PH_(3) lt AsH_(3) lt NH_(3) lt SbH_(3)`-boiling point.
`NH_(3)` has higher boiling point due to `H-`bonding.In rest of the hydrides the boiling point increases down the group with increasing atomic number on account of the increasing magnitude of van der Waal's attraction.
van der Wall attraction `prop` molecular weight.
(b)`Bi^(3+) lt Sb^(3+) lt As^(3+)`-stability of `+3` oxidation state decreases down the group due to inert pair effect.
( c)`NH_(3) lt PH_(3) lt AsH_(3) lt SbH_(3) lt BiH_(3)`-reducing character increses down the group as bond dissociation energy decreases.