Systems which `"has"//"have"` not been correctly characterised is

Options

A. cubic, a = b = c, `alpha=beta=gamma= 90^@`
B. cubic, a = b =c, `alpha=beta=gamma ne 90^@`
C. monoclinic , `a ne b ne c`, `alpha=gamma=90^@` `beta ne 90^@`
D. tetragonal, `a = b ne c`, `alpha=beta=gamma=90^@`.

Explanation

To solve the question regarding the incorrect characterization of crystal systems, we will analyze each system one by one based on their defining characteristics.

### Step-by-Step Solution:

1. **Understanding Cubic System:**
- In a cubic crystal system, all three edge lengths (a, b, c) are equal.
- All angles (α, β, γ) are equal to 90 degrees.
- **Conclusion:** The first cubic system is correctly characterized.

2. **Analyzing the Second Cubic System:**
- The second system is also cubic, which means it should have a = b = c.
- However, it states that α = β = γ is not equal to 90 degrees.
- **Conclusion:** This characterization is incorrect because, in a cubic system, all angles must be 90 degrees.

3. **Examining Monoclinic System:**
- For the monoclinic system, the characteristics are:
- a ≠ b ≠ c
- α = γ = 90 degrees
- β ≠ 90 degrees
- **Conclusion:** This characterization is correct for monoclinic.

4. **Reviewing Tetragonal System:**
- In the tetragonal system:
- a = b ≠ c
- α = β = γ = 90 degrees
- **Conclusion:** This characterization is also correct for tetragonal.

5. **Final Conclusion:**
- The only incorrect characterization found is in the second cubic system where the angles are not equal to 90 degrees. Therefore, the answer is the second option.

### Final Answer:
The system that has not been correctly characterized is the second cubic system.