Why an end-centred unit cell cannot he cubic? What is the highest possible symmetry for this type of unit cell?

Explanation

To answer the question "Why an end-centred unit cell cannot be cubic? What is the highest possible symmetry for this type of unit cell?", we can break it down into two parts:

### Step 1: Understanding the Structure of Unit Cells
1. **Cubic Unit Cell**: In a cubic unit cell, all the constituent particles (atoms, ions, or molecules) are located at the corners of the cube. In some cubic structures, there may also be particles at the center of the cube (body-centered) or at the centers of the faces (face-centered).

2. **End-Centred Unit Cell**: An end-centred unit cell has particles at the corners of the unit cell and an additional particle at the center of two opposite faces. This means that there are particles at the corners and at the center of two of the faces.

### Step 2: Why an End-Centred Unit Cell Cannot be Cubic
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