The oxidation number of $Cr$ in $K_2Cr_2O_7$ is

$A$ compound contains atoms $X$,$Y$,and $Z$. The oxidation number of $X$ is $+2$,$Y$ is $+5$ and $Z$ is $-2$. Therefore,a possible formula of the compound is

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

Amongst the following,identify the species with an atom in $+6$ oxidation state.

When $KMnO_4$ is reduced with oxalic acid in acidic solution,the oxidation number of $Mn$ changes from

In which of the following compounds does nitrogen exhibit the highest oxidation state?