What type of crystal defect is indicated in the diagram below?

An ionic compound has a unit cell consisting of $\mathrm{A}$ ion at the corners of a cube and $\mathrm{B}$ ions on the centres of the faces of the cube. The empirical formula for this compound would be

In a compound, atoms of element $\mathrm{Y}$ form ccp lattice and those of element $\mathrm{X}$ occupied of $\frac{2}{3}$rd of tetrahedal voids. The formula at the compound will be

$\mathrm{AB}$ crystallises in body centred cubic lattice with edge length, $\mathrm{a}$ equal to $387 \mathrm{pm}$. The distance between two oppositively charged ions in the lattice is