If AgCl is doped with $1 \times 10^{-4}$ mole percent of $\mathrm{CdCl}_2$ the number of cation vacancies (in $\mathrm{mol}^{-1}$ ) is

An element (atomic weight $=250 \mathrm{u}$ ) crystallises in a simple cubic lattice. If the density of the unit cell is $7.2 \mathrm{~g} \mathrm{~cm}^{-3}$. What is the radius (in $\mathop {\rm{A}}\limits^{\rm{o}}$ ) of the atom of the element?

$$ \left(N_A=6.02 \times 10^{23} \mathrm{~mol}^{-1}\right) $$

A compound is formed by two elements $A$ and $B$. Atoms of the element $B$ (as anion) make ccp lattice and those of element $A$ (as cation) occupy all tetrahedral voids. The formula of the compound is

An element crystallises in bcc lattice. The atomic radius of the element is $2.598 \mathop {\rm{A}}\limits^{\rm{o}}$. What is the volume (in $\mathrm{cm}^3$ ) of one unit cell?