It is given that, nickel oxide has the formula as Ni0.98O1.00 As per the formula, there are 98Ni ions for 100 oxide ions. Out of 98Ni ions, let x ions be in +2 oxidation state. (98−x) ions will be in +3 oxidation state. Oxide ion has −2 charge. To maintain electrical neutrality, total positive charge on cations = total negative charge on anions. 2x+3(98−x)+100(−2)=0 x=94 Fraction of Ni−2+ ions =‌
94
98
=0.96 Fraction of Ni3+ ions =‌
4
98
=0.04 Hence, the fractions of nickel that exists as Ni2+ and Ni3+ are Ni2+=96% and Ni3+=4% respectively.