If $HNO_3$ changes into $N_2O$,the oxidation number of nitrogen is changed by

What is the order of the oxidation number of $S$ in $SO_3^{2-}$,$S_2O_4^{2-}$,and $S_2O_6^{2-}$?

Assign oxidation number to the underlined elements in each of the following species:
$(a)$ $NaH_2\underline{P}O_4$
$(b)$ $NaH\underline{S}O_4$
$(c)$ $H_4\underline{P_2}O_7$
$(d)$ $K_2\underline{Mn}O_4$
$(e)$ $Ca\underline{O_2}$
$(f)$ $Na\underline{B}H_4$
$(g)$ $H_2\underline{S_2}O_7$
$(h)$ $KAl(\underline{S}O_4)_2 \cdot 12H_2O$

The oxidation number of carbon in $CH_2O$ is

What is the oxidation number of $S$ in $H_2S_2O_8$?

The oxidation number of carbon in graphite is ....... .