The order of heat of vaporisation or boiling point of the following hydrides of VA group elements is
$NH _{3}> BiH _{3}> SbH _{3}> AsH _{3}> PH _{3}$
Boiling point increase with increase in molecular mass hence, boiling point of $BiH _{3}$ should be maximum and that of $NH _{3}$ should be minimum. But $NH _{3}$ has highest boiling point because of $H$-bond present in $NH _{3}$.