Which one of the following crystals does not exhibit Frenkel defect?

Ionic solids,with Schottky defects,contain in their structure

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

As a result of Schottky defect,the density of the crystal:

Iron crystallizes in $FCC$ with an edge length of $400 \ pm$. If it contains $0.1 \%$ Schottky defects, calculate its approximate density $[AW \text{ of } Fe = 56 \ g/mol]$. (in $g/cm^3$)

Schottky defect is generally observed in which of the following?