What is the oxidation state of $S$ in $H_2SO_3$?

What is the change in the oxidation state of nitrogen when $HNO_3$ is converted into $N_2O$?

In which compound is the oxidation state of phosphorus $+4$?

Assign the oxidation number to the underlined element in each of the following species:
$1$. $K_2\underline{Mn}O_4$
$2$. $Ca\underline{O}_2$
$3$. $Na\underline{B}H_4$
$4$. $KAl(\underline{S}O_4)_2 \cdot 12H_2O$

In alkaline condition,$KMnO_4$ reacts as $2KMnO_4 + 2KOH \to 2K_2MnO_4 + H_2O + [O]$. The equivalent weight of $KMnO_4$ would be (Atomic mass of $K = 39$,$Mn = 55$,$O = 16$).

Oxidation number of potassium in $K_2O$,$K_2O_2$ and $KO_2$,respectively,is