Chromium plating can involve the electrolysis of an electrolyte of an acidified mixture of chromic acid and chromium sulphate. If during electrolysis the article being plated increases in mass by `2.6g` and `0.6dm^(3)` of oxygen are evolved at an inert anode, the oxidation state of chromium ions being discharged must be `: (` assuming atomic weight of `Cr=52` and `1 mol e` of gas at room temperature and pressure occupies a volume at `24dm^(3))`