Question

Number of moles of unit cells present in $40g$ of solid $\left(AB\right)$ (formula mass of $AB=10$) having rock salt type structure is________.

Answer 1

Number of moles of unit cells present in 40 g of solid (AB) (formula mass of AB=10) having rock salt type structure is 1.
Rock salt (NaCl) type structure has fcc arrangement with 4 formula units of solid AB present per unit cell.
Weight of solid $=40$ g
Molecular weight of solid $=10$ g/mol
Number of moles of solid $=\frac{40g}{10g/mol}=4moles$
Number of moles of unit cells $=\frac{\text{number of moles}}{4}=\frac{4}{4}=1$