Discussion on IIT-JEE

 This is formed as hexagonal stacked layers with coordination number = 12. There are 6 atoms in the hcp unit cell. The hex shape has six atoms at the points that are direct translations of each other making 1 atom for the top hex and one atom for the bottom hex. The atom in the center of the top and center of the bottom are translations giving 1 more. Then there are 3 atoms in the middle region of each cell bringing the total to 6.
In the primitive hexagonal cell we have 1 atom at each of the corners of the cell (each is "worth" 1/8) and 1 atom within the cell giving us 2 atoms/unit cell.