$A$ group $15$ element forms $d \pi - d \pi$ bond with transition metals. It also forms a hydride,which is the strongest base among the hydrides of other group members that form $d \pi - d \pi$ bonds. The atomic number of the element is $.......$

Which of the following elements does not exhibit the inert pair effect?

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.

$H_3PO_4$ $\xrightarrow{250\ ^oC}$ $(X)$ $\xrightarrow{600\ ^oC}$ $(Y)$
$H_3PO_4$ $\xrightarrow{600\ ^oC}$ $(Y)$
$(X)$ and $(Y)$ are:

$A$ hydride of nitrogen which is acidic is

Which of the following has the lowest boiling point?