Average oxidation state of Br in ${\mathrm{Br}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{8}}$ is $\frac{\text{2x}}{\text{3}}$.Then x is ___

the oxidation state of both the terminal bromine atoms will be +6
The central atom is joined to 2 oxygen atoms. So, the oxidation state of the central bromine will be = +4.
Hence, the average oxidation of bromine is :  $16/3\mathrm{or}2\left(8\right)/3$