Analysis shows that Nickel oxide has the formula ${\mathrm{Ni}}_{0.98}{\mathrm{O}}_{1.00}$ What is the fraction of Nickel that exist as  ${\mathrm{Ni}}^{+2}?$ 

It is given that nickel oxide has the formula as Ni_0.98​O_1.00​.

As per the formula, there are 98 Ni ions for 100 oxide ions.

Out of 98 Ni 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 Ni²⁺ ions = $\frac{94}{98}=0.96$

Fraction of Ni⁺³ ions = $\frac{98-94}{98}=0.04$

$\therefore$The fraction of Nickel that exist as  ${\mathrm{Ni}}^{+2}=0.96\times 100=96\%$