Example of unit cell with crystallographic dimensions
`a!=b!=c, alpha=beta=gamma=90^(@)` 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 crystallographic dimensions where \( a \neq b \neq c \) and \( \alpha = \beta = \gamma = 90^\circ \), we will analyze the provided options step by step.

### Step 1: Understand the given conditions
The conditions specify that:
- The lengths of the edges of the unit cell are not equal: \( a \neq b \neq c \).
- All the angles between the edges are right angles: \( \alpha = \beta = \gamma = 90^\circ \).

### Step 2: Analyze the options
1. **Calcite**:
- Calcite is a rhombohedral structure where all edge lengths are equal (\( a = b = c \)) and all angles are equal to 90 degrees.
- **Conclusion**: This option does not satisfy the conditions.

2. **Graphite**:
- Graphite has a hexagonal structure where \( a = b \) but \( b \neq c \), and the angles are \( \alpha = \beta = 90^\circ \) and \( \gamma = 120^\circ \).
- **Conclusion**: This option does not satisfy the conditions.

3. **Rhombic Sulphur**:
- Rhombic sulphur is an example of an orthorhombic structure where \( a \neq b \neq c \) and \( \alpha = \beta = \gamma = 90^\circ \).
- **Conclusion**: This option satisfies all the conditions.

4. **Monoclinic Sulphur**:
- Monoclinic structures have \( a \neq b \neq c \) but \( \beta \) is not equal to 90 degrees (it is typically greater or less than 90 degrees).
- **Conclusion**: This option does not satisfy the conditions.

### Step 3: Final Conclusion
Based on the analysis of the options, the only unit cell that fits the criteria of \( a \neq b \neq c \) and \( \alpha = \beta = \gamma = 90^\circ \) is **Rhombic Sulphur**.

### Answer:
The example of a unit cell with crystallographic dimensions \( a \neq b \neq c \) and \( \alpha = \beta = \gamma = 90^\circ \) is **Rhombic Sulphur**.

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