Among the unit cells given below, which two are highly symmetric and unsymmetric respectively

Options

A. Hexagonal, cubic
B. Orthorhombic, cubic
C. Cubic, triclinic
D. Monoclinic, cubic

Answer

To solve the question of identifying the highly symmetric and unsymmetric unit cells among the given options, we will follow these steps:

### Step-by-Step Solution:

1. **Understanding Unit Cells**:
- A unit cell is the smallest repeating unit in a crystal lattice that reflects the symmetry and structure of the entire crystal.

2. **Identifying Symmetry in Unit Cells**:
- Symmetry in unit cells can be analyzed based on the lengths of the edges (A, B, C) and the angles between them (α, β, γ).
- A highly symmetric unit cell will have equal edge lengths and angles.

3. **Cubic Unit Cell**:
- In a cubic unit cell, all three edge lengths are equal (A = B = C) and all angles are 90 degrees (α = β = γ = 90°).
- This makes the cubic unit cell highly symmetric.

4. **Tri-clinic Unit Cell**:
- In a tri-clinic unit cell, the edge lengths are all different (A ≠ B ≠ C) and the angles are also different (α ≠ β ≠ γ) and none of the angles are 90 degrees.
- This lack of uniformity in edge lengths and angles makes the tri-clinic unit cell highly unsymmetric.

5. **Conclusion**:
- Based on the analysis, the highly symmetric unit cell is the **Cubic** unit cell, and the highly unsymmetric unit cell is the **Tri-clinic** unit cell.

### Final Answer:
- **Highly Symmetric Unit Cell**: Cubic
- **Highly Unsymmetric Unit Cell**: Tri-clinic