The elements of symmetry in a crystal are

Options

A. plane of symmetry
B. axis of symmetry
C. centre of symmetry
D. None of the above

Answer

To solve the question regarding the elements of symmetry in a crystal, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Symmetry in Crystals**:
- Symmetry in crystals refers to the orderly and repetitive arrangement of atoms in a crystal lattice. The elements of symmetry help describe how the crystal structure can be divided or rotated to yield identical halves.

2. **Identifying the Types of Symmetry**:
- There are three main types of symmetry elements in crystals:
- **Plane of Symmetry**: A hypothetical plane that divides the crystal into two mirror-image halves. If you were to fold the crystal along this plane, both halves would match perfectly.
- **Axis of Symmetry**: An imaginary line around which the crystal can be rotated by a certain angle (e.g., 90°, 120°, etc.) and still appear the same. For example, a 4-fold axis means that rotating the crystal by 90° will yield the same appearance.
- **Center of Symmetry**: A point in the crystal where for every point at a distance from this center, there is an equivalent point at the same distance in the opposite direction. This means that the crystal is symmetrical about this central point.

3. **Analyzing the Options**:
- The question provides options:
- A) Plane of symmetry
- B) Axis of symmetry
- C) Center of symmetry
- D) None of them
- Since we have identified that all three types of symmetry (A, B, and C) exist in crystals, we can conclude that options A, B, and C are correct.

4. **Conclusion**:
- Therefore, the answer to the question is that the elements of symmetry in a crystal are: **Plane of symmetry, Axis of symmetry, and Center of symmetry**.

### Final Answer:
The elements of symmetry in a crystal are:
- Plane of symmetry
- Axis of symmetry
- Center of symmetry