Assertion (A): When a solution of `CH_(3)COOH` in water is shaken with charcoal, `pH` of the solution will get decreased.
Reason (R) : The degree of ionisation of `CH_(3)COOH` increase.

Options

A. If both (A) and (R) are correc, 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 incorrect, but (R) is correct.

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that when a solution of acetic acid (CH₃COOH) in water is shaken with charcoal, the pH of the solution will decrease.
- Acetic acid is a weak acid that partially ionizes in water to produce H⁺ ions and CH₃COO⁻ ions.

2. **Effect of Charcoal on the Solution**:
- When charcoal is added to the acetic acid solution, it adsorbs H⁺ ions from the solution.
- As H⁺ ions are removed from the solution, the concentration of H⁺ ions decreases.

3. **Understanding pH**:
- The pH of a solution is defined as pH = -log[H⁺].
- If the concentration of H⁺ ions decreases, the pH value will actually increase (not decrease).

4. **Conclusion on Assertion**:
- Therefore, the assertion that the pH will decrease is **false**. Instead, the pH will increase because the concentration of H⁺ ions is reduced due to adsorption by charcoal.

5. **Understanding the Reason (R)**:
- The reason states that the degree of ionization of acetic acid will increase when shaken with charcoal.
- As H⁺ ions are adsorbed by charcoal, the equilibrium of the ionization reaction (CH₃COOH ⇌ H⁺ + CH₃COO⁻) will shift to the right to produce more H⁺ ions to counteract the decrease in concentration (Le Chatelier's Principle).

6. **Conclusion on Reason**:
- Therefore, the reason that the degree of ionization of acetic acid increases is **true**.

7. **Final Evaluation**:
- Since the assertion is false and the reason is true, the correct answer is that A is incorrect but R is correct.

### Final Answer:
- Assertion (A) is false, and Reason (R) is true.