Which element of group $-15$ forms the most basic hydride with hydrogen?

Nitrogen forms $N_2$,but phosphorus prefers to exist as $P_4$ rather than $P_2$. Which of the following is the reason for this?

Strong reducing behaviour of $H_3PO_2$ is due to

Which of the following elements of group $15$ $(VA)$ does not show allotropy?

In the modern process,phosphorus is manufactured by:

When $NH_3$ reacts with $Cl_2$,which of the following statements are correct?
$(a)$ $NCl_3$ is formed when $Cl_2$ is in excess.
$(b)$ $N_2$ is formed when $Cl_2$ is in excess.
$(c)$ $N_2$ is formed when $NH_3$ is in excess.
$(d)$ $NCl_3$ is formed when $NH_3$ is in excess.