Which one of the following contains a $P-O-P$ bond?

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T.$:
$\underline{N}F_3 + H_2O \longrightarrow \text{No reaction}$

With reference to protonic acids,which of the following statements is correct?

Which of the following is a mixed anhydride?

Strong reducing behaviour of $H_3PO_2$ is due to

The gases liberated when zinc reacts with dilute and conc. $HNO_3$ respectively are