Experimentally it was found that a metal oxide has formula M_0.98O. Metal M, is present as M²⁺ and M³⁺ in its oxide. Fraction of the metal which exists as M³⁺ would be

 oxygen is in the oxidation state of -2, In order for M_0.98 to be neutral, its total oxidation state must be +2.
Let x represent the fraction of M³⁺.
M²⁺ fraction will then be (0.98-x).
When the compound becomes neutal,
$\begin{array}{l}3x+2(0.98-x)=2\\ 3x+1.96-2x=2\\ x=2-1.96\\ x=0.04\end{array}$

Therefore, the correct answer is 0.04