$A$ hydride of nitrogen which is acidic is

$Y$ in the given sequence of reactions is
$P_4 + x NaOH + y H_2O \xrightarrow{CO_2} X + z NaH_2PO_2$
$X + CuSO_4 \rightarrow Y + H_2SO_4$

The stability of $+1$ oxidation state increases in the sequence:

Pure nitrogen can be prepared from

Correct statements from the following are: $A$. Nitrogen in oxidation states from $+1$ to $+4$ disproportionates in acid medium. $B$. Nitrogen has the ability to form $d\text{--}p$ multiple bonds with itself and other elements with small size and high electronegativity. $C$. $N$-$N$ single bond is stronger than $P$-$P$ single bond. $D$. Nitrogen has highest density in its group due to small size. $E$. The maximum covalency of nitrogen is four since it has only four valence orbitals for bonding.

Which oxide is alkaline?