Which of the following crystals exhibits both Schottky and Frenkel defects?

The formula of nickel oxide is $Ni_{0.98}O_{1.00}$. What is the approximate percentage of $Ni^{2+}$ in it?

Given below are two statements.
Statement $I:$ Frenkel defects are vacancy as well as interstitial defects.
Statement $II:$ Frenkel defect leads to colour in ionic solids due to presence of $F$-centres.
Choose the most appropriate answer for the statements from the options given below:

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

The defect produced due to the presence of extra cations at interstitial sites is called

If $NaCl$ is doped with $10^{-3} \ mol \ \%$ $SrCl_2$,then the concentration of cation vacancies will be