Experimentally it was found that a metal oxide has formula M0.98O. Metal M, is present as M2+ and M3+ in its oxide. Fraction of the metal which exists as M3+ would be

Let the fraction of metal which exists as M3+ be x. Then the fraction of metal exists as M2+ = (0.98 - x)∴    3x+2(0.98−x)=2                  x+1.96=2                           x=0.04∴              % of M3+=0.040.98×100=4.08%