Assertion : The density of water remains constant as it is cooled from room temperature untill its temperature reached `4^(@)C`.
Reason : Below `4^(@)C`, the density increases.

Options

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

Explanation

To analyze the assertion and reason provided in the question, we will break down the statements step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "The density of water remains constant as it is cooled from room temperature until its temperature reaches 4°C."
- To evaluate this, we need to consider how the density of water changes with temperature. As water is cooled from room temperature (around 20-25°C) to 4°C, it actually experiences a decrease in volume, which leads to an increase in density. Therefore, this assertion is **false**.

2. **Understanding the Reason**:
- The reason states that "Below 4°C, the density increases."
- In reality, when water is cooled below 4°C, it begins to expand, which means its volume increases. Since density is defined as mass divided by volume (Density = Mass/Volume), an increase in volume while the mass remains constant leads to a decrease in density. Thus, this reason is also **false**.

3. **Conclusion**:
- Both the assertion and the reason are incorrect. Therefore, the correct answer is that both statements are false.

### Final Answer:
Both the assertion and the reason are false.