If $10^{-4} \% SrCl_2$ is added to a crystal of $NaCl$,find the number of cationic vacancies created in the crystal.

Explain metal excess defects.

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

Assertion : Due to Frenkel defect,there is no effect on the density of the crystalline solid.
Reason : In Frenkel defect,no cation or anion leaves the crystal.

Which of the following statements are not correct?
$(A)$ Diode is a combination of $n$-type and $p$-type semiconductors.
$(B)$ Silicon or germanium is electron rich impurity.
$(C)$ Phosphorus and arsenic are electron deficient impurities.
$(D)$ Schottky defect decreases the density of the crystal.

Which of the following molecular formula and type of defect are correct for the following statement?
"In $FeO$ crystal,some $Fe^{2+}$ ions are missing and the loss of positive charge is made up by the presence of $Fe^{3+}$ ions".