The oxidation state of $Cr$ in $Cr_2O_7^{2-}$ is

The oxidation number of carbon in $CH_3Cl$ is:

Consider the following molecules: $Br_3O_8$,$F_2O$,$H_2S_4O_6$,$H_2S_5O_6$,and $C_3O_2$. Count the number of atoms existing in their zero oxidation state in each molecule. Their sum is . . . . .

$A$ metal ion $M^{3+}$ after the loss of three electrons in a reaction will have an oxidation number equal to

The oxidation number of $Mn$ in $MnO_4^{-}$ is

Oxidation number of $Mn$ in $K_2MnO_4$ and in $KMnO_4$ are respectively