For which element would $XH_3$ be a stable species?

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T.$:
$\underline{P}Cl_5 + H_2O \longrightarrow H_3PO_4 + HCl$

Given below are two statements:
Statement-$I$: Element '$X$' and '$Y$' are the most and least electronegative elements, respectively, among $N, As, Sb$ and $P$. The nature of the oxides $X_{2}O_{3}$ and $Y_{2}O_{3}$ is acidic and amphoteric, respectively.
Statement-$II$: $BCl_{3}$ is covalent in nature and gets hydrolysed in water. It produces $[B(OH)_{4}]^{-}$ and $HCl$ in aqueous medium.

How many $P-O-P$ linkages are there in $P_4O_{10}$?

$PCl_5$ exists but $NCl_5$ does not because:

Assertion $(A)$: $P_4O_{10}$ cannot be used to remove moisture from ammonia gas. Reason $(R)$: $P_4O_{10}$ reacts with $NH_3$ gas. The correct answer is: