Calculate the oxidation number of $Cr$ in $CrO_4^{2-}$ ion and $K_2Cr_2O_7$ respectively.

Calculate the correct increasing order of average oxidation number of sulphur in $S_8, S_2O_3^{2-}, S_2O_7^{2-}, S_4O_6^{2-}, SO_3^{2-}$

Calculate the consecutive oxidation numbers of $Br$ in $Br_3O_8$.

In the chromyl chloride test for the confirmation of $Cl^{-}$ ion,a yellow solution is obtained. Acidification of the solution and the addition of amyl alcohol and $10\% H_2O_2$ turns the organic layer blue,indicating the formation of chromium pentoxide. The oxidation state of chromium in that compound is:

What is the oxidation number of nitrogen in $N_3H$?

The oxidation states of $S$ in Peroxodisulphuric acid $(H_2S_2O_8)$ and Sodium tetrathionate $(Na_2S_4O_6)$ are respectively: