Question

The boiling points of the following hydrides follow the order of:

• A. $NH _{3}> AsH _{3}> PH _{3}> SbH _{3}$
• B. $SbH _{3}> AsH _{3}> PH _{3}> NH _{3}$
• C. $SbH _{3}> NH _{3}> AsH _{3}> PH _{3}$
• D. $NH _{3}> PH _{3}> AsH _{3}> SbH _{3}$

Answer 1

Answer: (C)

Compounds $NH _{3} \,\, PH _{3}\,\, AsH _{3}\,\, SbH _{3}$Boiling point (in K) $238 \,\,185 \,\,211 \,\,254$
(i) From $PH _{3}$ to $SbH _{3}$ boiling point increases regularly due to increase in van der Waals forces of attraction.
(ii) $NH _{3}$ has exceptionally high boiling point due to hydrogen bonding.
$\therefore $ The boiling points are of the order
$SbH _{3}> NH _{3}> AsH _{3}> PH _{3}$