Point defects

In a metal deficient oxide sample, $\mathbf{M_XY_2O_4}$ (M and Y are metals), M is present in both +2 and +3 oxidation states and Y is in +3 oxidation state. If the fraction of $\mathbf{M^{2+}}$ ions present in M is $\dfrac13$, the value of X is _____.

Metal deficiency defect is shown by $\mathrm{Fe_{0.93}O}$. In the crystal, some $\mathrm{Fe^{2+}}$ cations are missing and loss of positive charge is compensated by the presence of $\mathrm{Fe^{3+}}$ ions. The percentage of $\mathrm{Fe^{2+}}$ ions in the $\mathrm{Fe_{0.93}O}$ crystals is ______. (Nearest integer)

The incorrect statement about the imperfections in solids is :

The appearance of colour in solid alkali metal halides is generally due to :

The correct statement(s) regarding defects in solids is(are)