Which element does not show allotropy:

$A$ tetra-atomic molecule $(A)$ on reaction with excess oxygen produces substance $(B)$. $(B)$ is a dehydrating agent. The substances $(A)$ and $(B)$ respectively will be:

$PCl_{5} + P_{4}O_{10} \xrightarrow{\Delta } X$. The product $(X)$ is an oxygen-containing compound. How many moles of an oxyacid are formed on the complete hydrolysis of $1 \text{ mole}$ of $(X)$?

The reaction,which forms nitric oxide $(NO)$,is

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

Which statement is false?