Analysis shows that nickel oxide has the formula $N{i}_{0.98}{O}_{1.00}.$  The fractions of Ni²⁺ and Ni³⁺ ions in the crystal are  

 $N{i}_{0.98}{O}_{1.00}have98Niions\&100O^{-2}ions$
Total cation charge = Total Anion charge
 $2x+294-3x=200\Rightarrow x=94$
 $\begin{array}{l}N{i}^{+2}ions=94andN{i}^{+3}ions=4\\ FractionofN{i}^{+2}=\frac{94}{98}=0.96\%N{i}^{+2}=96\%\\ N{i}^{+3}=\frac{4}{98}=0.04\%N{i}^{+3}=4\%\end{array}$