The basic character of hydrides of the `V`-group elements decreases in the order

The basic character of hydrides of the VB group elements decreases in the order:

The basic strength of the hydrides of group 15 elements :

The reducign character fo the hydrides of group - 15 elements increase down the group form NH_(3) to BiH_(3) - why?

The boiling point of hydrides of group 16 elements are in the order.

The boiling points of hydrides of group 16 elements are in the order :