Which element of group $15$ forms the most basic compound with hydrogen?

Phosphonic acid $(H_3PO_3)$ is:

In which of the following is $NH_3$ $NOT$ used?

In the following reaction,identify the nature of the products formed by the complete hydrolysis of $\underline{P}_4O_8$ at $R.T$:
$\underline{P}_4O_8 + H_2O \longrightarrow H_3PO_3 + H_3PO_4$

How many compounds given below are amphoteric oxides?
$P_2O_5, P_4O_6, As_2O_5, As_4O_6, Sb_2O_5, Sb_4O_6, Bi_2O_3$

Nitrogen gas is liberated by thermal decomposition of