Assertion : An electrostatic precipitator (ESP) is a particulate collection device that removes dust and smoke particles from flowing air using the force of an induced electrostatic charge.
Reason : An ESP is a highly efficient device as it removes 99 percent of particulate matter present in the exhaust from a thermal power plant.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that an electrostatic precipitator (ESP) is a device that removes dust and smoke particles from air using electrostatic charge. This is true because ESPs work by charging particles and collecting them on plates.

**Hint**: Recall the basic function of an electrostatic precipitator and its role in air pollution control.

2. **Understanding the Reason**:
- The reason given is that an ESP is highly efficient, removing 99% of particulate matter from thermal power plant exhaust. This statement is also true, as ESPs are designed to capture a significant amount of particulates.

**Hint**: Think about the efficiency of air pollution control devices and how they are measured.

3. **Evaluating the Relationship**:
- While both the assertion and reason are true, we need to determine if the reason correctly explains the assertion. The assertion describes what an ESP is and its function, while the reason provides a statistic about its efficiency. They are related in context but do not directly explain one another.

**Hint**: Consider whether the reason provides a direct explanation for the assertion or if it simply states a fact about the device.

4. **Conclusion**:
- Both the assertion and reason are true, but the reason is not the correct explanation of the assertion. Therefore, the correct answer is that both statements are true, but the reason does not explain the assertion.

**Hint**: Summarize your findings by stating the truth of both statements and their relationship.

### Final Answer:
- Both the assertion and reason are true, but the reason is not the correct explanation of the assertion.