$F$-centres are formed in $NaCl$ crystal if it is heated with $Na$ vapour. The above is due to

Zinc oxide (white) is heated to high temperature for some time. Observe the following statements regarding the above process:
$I$. Zinc oxide colour changes to pale yellow
$II$. The type of defect formed is 'metal deficiency'
$III$. Some $Zn^{2+}$ and $e^{-}$ are present in interstitial places
The correct statements are:

State the types of point defects.

In a solid lattice,the cation has left a lattice site and is located at an interstitial position. The lattice defect is:

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

If $NaCl$ is doped with $10^{-4} \ mol \%$ of $SrCl_2,$ the concentration of cation vacancies will be $(N_A = 6.02 \times 10^{23} \ mol^{-1}).$