Which of the following phosphorus oxyacids can act as a reducing agent?

The chemical formula for the phosphorus molecule is:

The electronegativity of a group $13$ element '$E$' is the same as that of $Ge$ (on the Pauling scale and up to one decimal point). The $CORRECT$ statements about $E^{3+}$ are:
$A$. It can act as a reducing agent.
$B$. It can act as an oxidizing agent.
$C$. $E^{3+}$ is more stable than $E^+$.
$D$. The standard electrode potential value for $E^{3+}/E$ is positive.

$PCl_5$ is well known,but $NCl_5$ is not. Why?

Pure $N_2$ is not produced when

Consider the following molecules $NH_3, PH_3, AsH_3, SbH_3$. Which of the following has the highest boiling point?