Assertion : Heavy metals such as cadmium, mercury, nickel etc. are water pollutants .
Reason : Heavy metals are not harmful to humans.

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 but reason is not the c orrect explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that heavy metals such as cadmium, mercury, and nickel are water pollutants.
- This is true because these metals are often released into water bodies from industrial processes, mining, and improper waste disposal. They can accumulate in aquatic ecosystems and pose significant risks to both environmental and human health.

2. **Understanding the Reason**:
- The reason states that heavy metals are not harmful to humans.
- This statement is false. Heavy metals like cadmium, mercury, and nickel are known to be toxic to humans. They can cause various health issues, including damage to the kidneys, liver, and nervous system, and can lead to long-term health problems.

3. **Conclusion**:
- Since the assertion is true and the reason is false, we conclude that the correct answer to the question is that the assertion is true, but the reason is false.

### Final Answer:
- The assertion is true, and the reason is false. Therefore, the correct option is C.