Which one of the following hydrides is least stable?

When concentrated nitric acid is heated,it decomposes to give

In pyrophosphorous acid,the number of $P-OH$,$P-H$,and $P=O$ linkages are respectively:

Which of the following allotropes of phosphorus is the most stable?

Which of the following oxoacids of phosphorus has the lowest oxidation state of phosphorus?

Explain the nature of hydride compounds of group-$15$ elements. Explain the nature of oxide compounds of group-$15$ elements. Write a note on halide compounds of group-$15$ elements.