What is the formula of the manganate ion?

The formal oxidation numbers of $Cr$ and $Cl$ in the ions $Cr_2O_7^{2-}$ and $ClO_3^{-}$ respectively are

Calculate the oxidation number of each sulfur atom in the following compounds:
$Na_2S_2O_3$
$Na_2S_4O_6$
$Na_2SO_3$
$Na_2SO_4$

Give the rules for the calculation of oxidation number.

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 oxidation states of $S$ atoms in Caro's acid and Marshall's acid are