Analysis show that nickel oxide consists of nickel ion with 96% ions having d⁸ configuration and 4% having d⁷ configuration. Which amongst the following best represents the formula of the oxide?

Ni = 3d⁸4s² (At. no. : 28), 

$\therefore$ Ni²⁺=3d⁸ and Ni³⁺=3d⁷

Hence, 96% ion of Ni²⁺ and 4% ions of Ni³⁺ are present. 

Let number of O^2- ion present in the crystal = x. 

Applying electroneutrality rule, 

Total positive charge = Total negative charge 

96 x 2 (+ve charge) = 4 x 3 (+ve charge) 

                                 = x $\times$ 2 (-ve charge) 

96 x 2 + 4 x 3 - 2x = 0 

$\therefore$x = 1.02 

So formula of crystal Ni_1.00O_1.02 or Ni_0.98O_1.00