Assertion (A): When carbon dioxide gas is passed through lime water, lime water is turned milky.
Reason (R): Calcium carbonate is soluble in water.

Options

A. Both (A) and (R) are true and (R) is the correct explanation for (A).
B. Both (A) and (R) are true but (R) is not the correct explanation for (A).
C. (A) is correct but (R) is false.
D. (A) is false but (R) is true.

Explanation

To solve the 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 when carbon dioxide (CO2) gas is passed through lime water, the lime water turns milky.
- Lime water is a solution of calcium hydroxide (Ca(OH)2). When CO2 is bubbled through it, a chemical reaction occurs.

2. **Chemical Reaction**:
- The reaction between carbon dioxide and lime water can be represented as:
\[ \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} \]
- In this reaction, calcium carbonate (CaCO3) is formed, which is a white precipitate.

3. **Observation**:
- The formation of calcium carbonate causes the lime water to turn milky, confirming that the assertion is true.

4. **Understanding the Reason (R)**:
- The reason states that calcium carbonate is soluble in water.
- However, calcium carbonate is actually **insoluble** in water, which means this statement is false.

5. **Conclusion**:
- Since the assertion is true (lime water turns milky when CO2 is passed through it) and the reason is false (calcium carbonate is not soluble in water), we can conclude that:
- Assertion (A) is true.
- Reason (R) is false.

6. **Final Answer**:
- The correct option is that the assertion is true, but the reason is false.