QJEEAdv08Ch6a25: JEE Advanced 2008 Chemistry - Class 12 JEEAdv08Ch6a25 Solution: The number of atoms in this HCP unit cell is :

The number of atoms in a HCP unit cells is 6.

3 atoms are at the middle of the unit cell and each atom contributes 1 atom to the unit cell.

2 atoms are at the two face centres of the unit cell and each atom contributes 1/2 atom to the unit cell.

12 atoms are at the 12 corners of the unit cell and each atom contributes 1/6 atom to the unit cell.

The number of atoms in one unit cell

(3 $\times$ 1) + (2 $\times$ 1/2) + (12 $\times$ 1/6) = 3 + 1 + 2 = 6