The oxidation number of sulphur in $H_2S$ is

The oxidation state of $Fe$ in $Fe_3O_4$ is:

The oxidation number of $C$ in $HNC$ is:

The oxidation number of $P$ in $KH_2PO_2$ is:

Oxidation number of $P$ in $Mg_2P_2O_7$ is

$A$ compound contains three elements $A$,$B$,and $C$. If the oxidation numbers are $A = +2$,$B = +5$,and $C = -2$,the possible formula of the compound is: