What is the highest oxidation state possessed by phosphorus in its oxyacids?

Extra pure $N_2$ can be obtained by heating :-

Choose the correct statements about the hydrides of group $15$ elements.
$A$. The stability of the hydrides decreases in the order $NH_3 > PH_3 > AsH_3 > SbH_3 > BiH_3$
$B$. The reducing ability of the hydrides increases in the order $NH_3 < PH_3 < AsH_3 < SbH_3 < BiH_3$
$C$. Among the hydrides,$NH_3$ is strong reducing agent while $BiH_3$ is mild reducing agent.
$D$. The basicity of the hydrides increases in the order $NH_3 < PH_3 < AsH_3 < SbH_3 < BiH_3$
Choose the most appropriate from the option given below:

With reference to protonic acids,which of the following statements is correct regarding the basicity of $PH_3$ and $NH_3$?

$NH_3 + O_2 \xrightarrow{\text{Catalyst}} NO + H_2O$. This step is used in which process?

Consider the reaction:
$P_4 + 3 NaOH + 3 H_2 O \rightarrow Q + 3 NaH_2 PO_2$
Identify the reaction in which $Q$ is not the product. (Equations are not balanced)