Question

among the hydride of group-15 elements which have the lowest boiling point

Answer 1

The correct answer should be - PH₃.

Although Nitrogen has the lowest molecular weight, it has a free pair of lone electrons that form bonds easily with the hydrogen atoms to form the hydrides. So, it has the highest boiling point amongst the Group 15 elements.

However, as we go across the table, the boiling points tend to increase with an increase in the molecular weights. As the molecular mass increases, the Vander Waal's forces also increase, which in turn increases the boiling points.

So, the correct order for boiling points in Group 15 elements is - 

NH₃ > PH₃ < AsH₃ < SbH₃ < BiH₃.

Answer 2

the correct answer is ph3