Example of unit cell with crystallographic dimensions `anebnec,alpha=gamma=90^(@),betane90^(@)` is

Options

A. Calcite
B. Graphite
C. Rhombic sulphur
D. Monoclinic sulphur

Answer

To solve the question regarding the example of a unit cell with specific crystallographic dimensions, we need to analyze the given conditions and options systematically.

### Step-by-Step Solution:

1. **Understanding the Crystallographic Dimensions**:
- The question specifies that the unit cell has dimensions \( a \neq b \neq c \) (meaning the lengths of the edges are all different).
- It also states that \( \alpha = \gamma = 90^\circ \) (the angles between the edges along the a and c axes are right angles).
- Finally, it mentions that \( \beta \neq 90^\circ \) (the angle between the edges along the b axis is not a right angle).

2. **Identifying the Type of Crystal System**:
- The conditions given correspond to the monoclinic crystal system. In monoclinic systems:
- The lengths of the edges can be different (\( a \neq b \neq c \)).
- Two angles are right angles (\( \alpha \) and \( \gamma \) are 90 degrees).
- The third angle (\( \beta \)) is not a right angle.

3. **Evaluating the Options**:
- **Option 1: Calcite** - This is a rhombohedral structure where all edge lengths are equal, and angles are equal (not matching our criteria).
- **Option 2: Graphite** - This is a hexagonal structure where \( a = b \) and \( \beta = 120^\circ \) (not matching our criteria).
- **Option 3: Rhombic Sulphur** - This is an orthorhombic structure where all angles are 90 degrees, and all edges can be different (not matching our criteria).
- **Option 4: Monoclinic Sulphur** - This matches our criteria as it has \( a \neq b \neq c \), \( \alpha = \gamma = 90^\circ \), and \( \beta \neq 90^\circ \).

4. **Conclusion**:
- Based on the analysis, the correct answer is **Option 4: Monoclinic Sulphur**.