Assertion : Secondary treatement of sewage is also called biological treatment while primary treatment is called physical treatment.
Reason : Primary sewage treatment depends only upon sedimentation properties of materials present in sewage and filtration.

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 correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that secondary treatment of sewage is referred to as biological treatment, while primary treatment is known as physical treatment.
- **Conclusion**: This statement is true because secondary treatment involves biological processes, mainly using microbes, to break down organic matter.

2. **Understanding the Reason**:
- The reason provided explains that primary sewage treatment relies solely on the sedimentation properties of materials in sewage and filtration.
- **Conclusion**: This statement is also true as primary treatment primarily involves physical processes such as filtration and sedimentation to remove solids from sewage.

3. **Linking the Assertion and Reason**:
- The reason given explains why primary treatment is classified as physical treatment. It highlights the absence of microbial action in this stage, which is a key characteristic that differentiates it from secondary treatment.
- **Conclusion**: Since the reason accurately explains the assertion, both the assertion and reason are true, and the reason is a correct explanation of the assertion.

4. **Final Conclusion**:
- Both the assertion and reason are true, and the reason is the correct explanation of the assertion.
- Therefore, the answer is: **Both assertion and reason are true, and the reason is the correct explanation of the assertion.**