Which of the following dissolves in hot conc. $NaOH$ solution?

Identify the incorrect statements about group $15$ elements :
$A$. Dinitrogen is a diatomic gas which acts like an inert gas at room temperature.
$B$. The common oxidation states of these elements are $-3, +3$ and $+5$.
$C$. Nitrogen has unique ability to form $p\pi-p\pi$ multiple bonds.
$D$. The stability of $+5$ oxidation states increases down the group.
$E$. Nitrogen shows a maximum covalency of $6$.
Choose the correct answer from the options given below.

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:

Of the following,the non-existent compound is

The strong reducing property of hypophosphorus acid $(H_3PO_2)$ is due to

Why are pentahalides of $P$,$As$,$Sb$,and $Bi$ more covalent than their trihalides?