Total volume of atoms present in a face-centred cubic unit cell of a metal is (r is atomic radius) :

Question

( A ) $\frac{24}{3} \pi r^2$
( B ) $\frac{20}{3} \pi r^2$
( C ) $\frac{16}{3} \pi r^2$
( D ) $\frac{12}{3} \pi r^2$