Calculate the increase or decrease in the oxidation state for each element listed as it changes from a reactant to a product. Use a negative sign to show a decrease in oxidation state.

sulfur, beginning in the reactant $ZnS$

sulfur, beginning in the reactant $H_{2}S$

chromium, beginning in the reactant $C{r}_2{O}_3$

$--------$

$$ Balanced equations:

$1)2$ZnS$($s$)+3($O$2)->2$ZnO$($s$)+2$ SO$2($g$)$

$2)$ Cu$^2($aq$)+$H$2$S$($g$)->$CuS$($s$)+2$H$($aq$)$

$3)3$Na$2$ O$2($s$)+$Cr$2$ O$3($s$)+2$H$+->6$Na$+($aq$)+2$CrO$4^2^{-}+$H$2$O$($l$)$