Question
When SO2 gas is bubbled in acidified (by H2SO4) aqueous solution of K2Cr2O7, a green coloured solution is formed above 50o C, which on evaporation crystalizes into a violet crystal which is used in the tanning of leather and in gelatin emulsions in photographic film as hardener. Find the oxidation state of sulphur in the complex formed, if oxidation state of chromium in the same complex is +3.