A atoms are present at body Centre. ∴ Number of atoms =1 Contribution of body Centre =1 ∴ Effective number of atoms A=1×1=1 B atoms are present at corners. ∴ Number of atoms at corners =8 Contribution of corner =
1
8
∴ Effective number of B=8×
1
8
=1 C atoms are present at half of face center's. ∴ Number of atoms =