Assertion : When a concentrated solution is diluted by adding more water , the number of moles of solute in the solution remains unchanged .
Reason : Number of a solute is equal to the product of molarity and volume of solution in litres.

Options

A. If both the assertion and reason are true statement and reason is correct explanation of the assertion .
B. If both the assertion and reason are true statement but reason is not a correct explanation of the assertion .
C. If the assertion is true but the reason is a false statement.
D. If both assertion and reason are false statements.

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that when a concentrated solution is diluted by adding more water, the number of moles of solute remains unchanged.
- This is a fundamental principle in chemistry: dilution does not change the amount of solute present, it only changes the concentration (molarity) and volume of the solution.

2. **Understanding the Reason**:
- The reason states that the number of moles of solute is equal to the product of molarity and volume of the solution in liters.
- This can be expressed mathematically as:
\[ n = M \times V \]
where \( n \) is the number of moles, \( M \) is the molarity, and \( V \) is the volume in liters.

3. **Analyzing the Effect of Dilution**:
- When we dilute a solution, we add water, which increases the volume \( V \).
- As the volume increases, the molarity \( M \) decreases because the same number of moles of solute is now in a larger volume.
- Therefore, even though \( M \) decreases, the product \( M \times V \) (which gives the number of moles) remains constant because the number of moles does not change.

4. **Conclusion**:
- Both the assertion and the reason are true statements.
- Furthermore, the reason correctly explains the assertion, as it provides the relationship between molarity, volume, and the number of moles.

### Final Answer:
- Both the assertion and reason are true, and the reason is the correct explanation of the assertion.