Solid State Questions

Experimentally it was found that a metal oxide has formula ${\text{M}}_{0.98}\text{O}$. Metal $\text{M}$ is present as ${\text{M}}^{2+}$ and ${\text{M}}^{3+}$ in its oxide. Fraction of the metal which exists as ${\text{M}}^{3+}$ would be:

Which of the following exists as covalent crystals in the solid state?