Which of the following given crystal system is the most symmetrical and the most unsymmetrical system respectively?

Options

A. Cubic, Hexagonal
B. Orthorhombic, Monoclinic
C. Cubic, Tridinic
D. Rhombohedral, Tetragonal

Answer

To determine which crystal systems are the most symmetrical and the most unsymmetrical, we need to analyze the properties of different crystal systems.

### Step 1: Identify the Symmetrical Crystal System
The most symmetrical crystal system is the **cubic system**. In a cubic system:
- The lengths of the axes are equal: \( a = b = c \).
- The angles between the axes are all equal to 90 degrees: \( \alpha = \beta = \gamma = 90^\circ \).

This uniformity in dimensions and angles gives the cubic system its high level of symmetry.

### Step 2: Identify the Unsymmetrical Crystal System
The most unsymmetrical crystal system is the **triclinic system**. In a triclinic system:
- The lengths of the axes are not equal: \( a \neq b \neq c \).
- The angles between the axes are not equal and are not 90 degrees: \( \alpha \neq \beta \neq \gamma \) and none of them are 90 degrees.

This lack of uniformity in dimensions and angles results in the triclinic system being the least symmetrical.

### Conclusion
Based on the analysis:
- The most symmetrical crystal system is the **cubic system**.
- The most unsymmetrical crystal system is the **triclinic system**.

Thus, the answer is **cubic and triclinic**.