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

The oxidation state of $Cr$ in $CrO_6$ is

What is the oxidation number of carbon in oxalic acid?

Assign the oxidation number to the underlined element in each of the following species:
$1$. $K_2\underline{Mn}O_4$
$2$. $Ca\underline{O}_2$
$3$. $Na\underline{B}H_4$
$4$. $KAl(\underline{S}O_4)_2 \cdot 12H_2O$

Write the oxidation number of oxygen in $KO_{3}$ and $Na_{2}O_{2}$.

The oxidation number of carbon in graphite is ....... .