Chemical nature of the nitrogen oxide compound obtained from a reaction of concentrated nitric acid and $P_{4}O_{10}$ (in $4:1$ ratio) is:

Which of the phosphorus oxoacids can create a silver mirror from $AgNO_3$ solution?

Which of the following is not hydrolysed?

Which is an incorrect match?

$NaH_2PO_4$ $\xrightarrow{230^\circ C}$ $Na_3P_3O_9$ $\xrightarrow{638^\circ C}$ $(NaPO_3)_n$ $\rightarrow D$ (glossy solid).
Compound $D$ is sodium hexametaphosphate,which is known as:

The decreasing values of bond angles from $NH_3$ $(106^o)$ to $SbH_3$ $(101^o)$ down group-$15$ of the periodic table is due to