Calculate the oxidation number of S in sulphate ion

Explanation

Standard hydrogen electrode
In standard hydrogen electrode, a platinum wire coated with finely divided platinum called platinum black is sealed in a glass tube. One end of glass tube is dipped in aqueous solution of 1 molar HCl. Pure hydrogen gas at 1 bar is bubbled through the tube at 298 K.
When SHE acts as anode, oxidation takes place as follows : `H_(2) (g) rarr 2H^(+) (aq) + 2e^(-)`
Whe SHE acts as cathode, reduction takes place as follows : `2H^(+) (aq) + 2e^(-) rarr H_(2)(g)`
The SHE is also known as reversible electrode because it can acts as anode as well as cathode.