Which of the following oxoacids of phosphorus has the lowest oxidation state of phosphorus?

Which of the following is oxidised in air?

In the following reaction sequence, the compound $C$ is $Al + N_2$ $\xrightarrow{\Delta} (A)$ $\xrightarrow{H_2O} B (ppt) + C_{(g)}$

In the $15^{th}$ group of the periodic table,the elements $N, P, As, Sb$,and $Bi$ are present. As we move from $N$ to $Bi$,how do the oxides with the general formula change?

Which of the following statements are correct?
$(I)$ $P_4$ molecule is very reactive because of angular strain.
$(II)$ The basicity of $H_3PO_3$ is $3$.
$(III)$ In gas phase,all $P-Cl$ bonds of $PCl_5$ have same bond length.
$(IV)$ In solid state,$PCl_5$ exists as an ionic solid,in which anion $[PCl_6]^-$ has octahedral and cation $[PCl_4]^+$ has tetrahedral shape.

The reaction of $P_4$ with $X$ leads selectively to $P_4O_6$. The $X$ is