Question

Which one of the following is a primitive unit cell?

• A. Simple cubic
• B. Body-centred cubic
• C. Face-centred cubic
• D. Both body-centred and face-centred cubic

Answer 1

The correct option is A Simple cubic

Unit cell are of two types :
1. Primitive unit cell
2. Centred unit cell

In primitive unit cells, constituent particles are present only on the corner positions of a unit cell.
Eg. Simple cubic
As shown, in simple cubic, atoms are present only at the corners.Thus, simple cubic is a primitive unit cell.


Centred unit cell:
A unit cell that contains one or more constituent particles present at positions other than corners, along with the corner particles.
Body centred cubic: Contains one constituent
particle (atom, molecule or ion) at its body-centre besides the ones at its corners.

Face-centred cubic: Constituent particles are present at the corners and at the centre of each face of the unit cell.

Thus, these are centred unit cells.