In which of the following acids,$P-P$ bond is present?

The number of $P-H$,$P-O-P$,$P-O-H$ and $P=O$ bonds in sodium dihydrogen pyrophosphate $(Na_2H_2P_2O_7)$ are respectively:

Consider the following reaction:
$A +$ alkali $\rightarrow B$ (Major Product)
If $B$ is an oxoacid of phosphorus with no $P-H$ bond,then $A$ is ..... .

$A$ pungent smelling gas $A$ gives dense white fumes with conc. $HCl$. When $A$ reacts with an alkaline solution of a colourless reagent $B$,a reddish-brown precipitate $C$ is formed. The compounds $A, B, C$ respectively are:

What is the product of the reaction between $HNO_3$ and $P_4O_{10}$?

Which nitrogen trihalide is the least basic?