Differentiate between primitive unit cell and centred unit cells.

Explanation

### Step-by-Step Solution:

1. **Definition of Primitive Unit Cell**:
- A primitive unit cell is defined as the smallest repeating unit in a crystal lattice that contains one or more atoms. In a primitive unit cell, the constituent particles (atoms) are located only at the corners of the unit cell.

2. **Example of Primitive Unit Cell**:
- The most common example of a primitive unit cell is the Simple Cubic Unit Cell (SCC). In this structure, there is one atom located at each of the eight corners of the cube. Since these corner atoms are shared among adjacent unit cells, the total number of atoms in a simple cubic unit cell is effectively one.

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