What is the oxidation number of $S$ in $SO_4^{2-}$?

What are the oxidation states of $P$ in $H_4P_2O_5$,$H_4P_2O_6$,and $H_4P_2O_7$ respectively?

$A$ 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:

The compound $YBa_2Cu_3O_7$,which shows superconductivity,has copper in an oxidation state of ........ Assume that the rare earth element Yttrium is in its usual $+3$ oxidation state.

The ionic charges of manganite and permanganate ion are respectively

In which of the following is the difference in the oxidation numbers of the underlined elements the greatest?