Assertion (A): The molecular mass of polymers cannot be calculated using the boiling point or freezing point method.
Reason (R ): The boiling point method for determining the molecular masses is used for compounds stable at high temperature.

Options

A. If both `(A)` and `(R )` are correct, and `(R )` is the correct explanation of `(A)`.
B. If both `(A)` and `(R )` are correct, but `(R )` is not the correct explanation of `(A)`.
C. If `(A)` is correct, but `(R )` is incorrect.
D. If `(A)` is correct, but `(R )` is correct.

Explanation

To solve the given question, we need to analyze the assertion and reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "The molecular mass of polymers cannot be calculated using the boiling point or freezing point method."
- This is true because polymers are large molecules, and their boiling point or freezing point changes are often too small to measure accurately.

2. **Understanding the Reason (R)**:
- The reason states that "The boiling point method for determining the molecular masses is used for compounds stable at high temperature."
- This is also true. The boiling point method is typically applied to small, stable molecules that can withstand high temperatures without decomposing.

3. **Evaluating the Relationship Between A and R**:
- We need to determine if R is a correct explanation of A.
- While both statements are correct, R does not directly explain why polymers cannot have their molecular mass determined using boiling point or freezing point methods. It simply states a condition about the boiling point method.

4. **Conclusion**:
- Since both A and R are correct, but R is not the correct explanation of A, the correct option is:
- Option B: Both A and R are correct, but R is not the correct explanation of A.

### Final Answer:
**Option B**: Both A and R are correct, but R is not the correct explanation of A.

---