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

The correct statement among the following,regarding defects in solids is:
$(1)$ Frenkel defect is favored by small difference in the sizes of cation and anion.
$(2)$ Frenkel defect is a metal excess defect.
$(3)$ Trapping of electron in the lattice leads to formation of $F$-centres.
$(4)$ Schottky defect has no effect on the physical property of solids.

If an electron is present in place of an anion in a crystal lattice,then it is called

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

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)

Calcium crystallises in a face-centred cubic unit cell with edge length $a = 0.556 \ nm$. Calculate the density. If it contained $0.1 \%$ Frenkel defects,what is the density in $g \ cm^{-3}$?