A solid contains elements $A$ and $B$. Anions of $B$ form ccp lattice. Cations of $A$ occupy 50\% of octahedral voids and 50\% of tetrahedral voids. What is the molecular formula of the solid?

A substance has a density of $2 \mathrm{~g} \mathrm{~cm}^{-3}$. It crystallises in the fcc crystal with an edge length of 600 pm . The molar mass of the substance (in $\mathrm{g} \mathrm{mol}^{-1}$ ) is $\left(N_A=6 \times 10^{23} \mathrm{~mol}^{-1}\right)$