Assertion(A): `Fe^(3+)` can be used for coagulation of `As_(2)S_(3)` sol.
Reason (R): `Fe^(3+)` reacts with `As_(2)S_(3)` to give `Fe_(2)S_(3.)`

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 the not the correct explanation of (A).
C. If (A) is correct, but (R) is incorrect.
D. If (A) is incorrect, but (R) is correct.

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that `Fe^(3+)` can be used for the coagulation of `As_(2)S_(3)` sol.
- `As_(2)S_(3)` is known to be a negatively charged colloidal sol. Colloids are stabilized by their charge, and in order to coagulate them, we need to neutralize that charge.

2. **Role of `Fe^(3+)`**:
- `Fe^(3+)` is a positively charged ion. When added to the negatively charged `As_(2)S_(3)` sol, it can neutralize the charge of the colloid.
- This neutralization leads to the destabilization of the colloid, causing the particles to come together and coagulate.

3. **Understanding the Reason (R)**:
- The reason states that `Fe^(3+)` reacts with `As_(2)S_(3)` to give `Fe_(2)S_(3)`.
- However, this reaction does not actually occur. `Fe^(3+)` does not react with `As_(2)S_(3)` to form `Fe_(2)S_(3)`. Instead, it simply neutralizes the charge of the colloidal particles.

4. **Conclusion**:
- The assertion is correct because `Fe^(3+)` can indeed be used for the coagulation of `As_(2)S_(3)` sol.
- The reason is incorrect because there is no reaction between `Fe^(3+)` and `As_(2)S_(3)` to form `Fe_(2)S_(3)`.
- Therefore, the correct answer is that the assertion is true, but the reason is false.

### Final Answer:
- Assertion (A) is correct.
- Reason (R) is incorrect.
- The answer is option C: Assertion is correct, Reason is incorrect.