Formula of nickel oxide with metal deficiency defect in its crystal is Ni_0.98 O. The crystal contains Ni^2+ and Ni^3+ ions. The fraction of nickel…

Formula of nickel oxide with metal deficiency defect in its crystal is $\displaystyle \mathrm{Ni}_{0.98} \mathrm{O}$. The crystal contains $\displaystyle \mathrm{Ni}^{2+}$ and $\displaystyle \mathrm{Ni}^{3+}$ ions. The fraction of nickel existing as $\displaystyle \mathrm{Ni}^{2+}$ ions in the crystal is -