Which of the following allotropes of phosphorus is the most stable?

The most stable hydride is

Which of the following is a cyclic phosphate?

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 one of the following is correct with respect to basic character?

The nitrogen oxide$(s)$ that contain$(s)$ $N-N$ bond$(s)$ is(are):
$A$. $N_2O$
$B$. $N_2O_3$
$C$. $N_2O_4$
$D$. $N_2O_5$