What does the structure of a solid containing a Schottky defect possess?

Which type of crystal defect is observed in the diagram given below?
$Na^{+} Cl^{-} Na^{+} Cl^{-} Na^{+} Cl^{-}$
$Cl^{-} \square Cl^{-} Na^{+} \square Na^{+}$
$Na^{+} Cl^{-} \square Cl^{-} Na^{+} Cl^{-}$
$Cl^{-} Na^{+} Cl^{-} Na^{+} \square Na^{+}$

Experimentally,it was found that a metal oxide has the formula $M_{0.98}O$. The metal $M$ is present as $M^{2+}$ and $M^{3+}$ in its oxide. The fraction of the metal which exists as $M^{3+}$ would be: .................... $\%$

Identify the defect that develops when the ratio of number of cations to anions becomes different from that indicated by its chemical formula.

Which of the following is $NOT$ a characteristic of Schottky defect?

Ionic solids,which have anionic vacancies due to metal excess defect,develop colour. Explain with the help of a suitable example.