Which of the following oxyacids contains both $P-H$ and $P-P$ bonds simultaneously?

Three allotropes $(A)$,$(B)$ and $(C)$ of phosphorus in the following change are respectively
$A \xrightarrow[1200 \ atm]{470 \ K} B$
$A \xrightarrow[CO_2 - atm]{570 \ K} C$

Find the correct statements related to group $15$ hydrides.
$A$. Reducing nature increases from $NH_3$ to $BiH_3$
$B$. Tendency to donate lone pair of electrons decreases from $NH_3$ to $BiH_3$
$C$. The stability of hydrides decreases from $NH_3$ to $BiH_3$
$D$. $HEH$ bond angle decreases from $NH_3$ to $SbH_3$ ($E$ = Elements of group $15$)
Choose the correct answer from the options given below:

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

Explain the chemical behaviour of oxoacids of phosphorus.

$FeSO_4$ forms a brown ring with which of the following?