A solid comprises of three types of elements, P, Q and R. P forms an FCC lattice in which Q and R occupy all the tetrahedral voids and half the octahedral voids respectively. The molecular formula of the solid is

A

$$\text{P}_2\text{Q}_4\text{R}$$

B

$$\text{PQ}_2\text{R}_4$$

C

$$\text{P}_4\text{Q}_2\text{R}$$

D

$$\text{P}_4\text{QR}$$