Study the given differences between primary sludge and activated sludge and select the incorrect ones. Primary Sludge Activated sludge (i) It is sludge formed during primary sewage treatment. It is sludge formed during secondary sewage treatment. (ii) It possesses flocs of decomposer microbes. It does not possess flocs of decomposer microbes. (iii) It does not require aeration. Formation of activated sludge requires aeration. (iv) A lot of decomposition occurs during formation of primary sludge. Very little decomposition occurs during formation of activated sludge.

Options

A. (i) and (ii)
B. (ii) and (iv)
C. (i),(ii) and (iv)
D. (ii) and (iii)

Explanation

To determine the incorrect statements between primary sludge and activated sludge, let's analyze each statement step by step:

### Step-by-Step Solution:

1. **Statement Analysis**:
- **Statement (i)**: "It is sludge formed during primary sewage treatment." (Primary Sludge) vs. "It is sludge formed during secondary sewage treatment." (Activated Sludge)
- **Analysis**: This statement is correct. Primary sludge is indeed formed during primary sewage treatment, while activated sludge is formed during secondary sewage treatment.

2. **Statement (ii)**: "It possesses flocs of decomposer microbes." (Primary Sludge) vs. "It does not possess flocs of decomposer microbes." (Activated Sludge)
- **Analysis**: This statement is incorrect. Primary sludge does not typically contain flocs of decomposer microbes because it is formed during the primary treatment, which primarily removes solids. Activated sludge, on the other hand, is rich in flocs of decomposer microbes as it is formed during the secondary treatment, where decomposition occurs.

3. **Statement (iii)**: "It does not require aeration." (Primary Sludge) vs. "Formation of activated sludge requires aeration."
- **Analysis**: This statement is correct. Primary sludge does not require aeration since it is formed by the physical removal of solids. In contrast, activated sludge formation requires aeration to support the growth of microbes that decompose organic matter.

4. **Statement (iv)**: "A lot of decomposition occurs during formation of primary sludge." (Primary Sludge) vs. "Very little decomposition occurs during formation of activated sludge."
- **Analysis**: This statement is incorrect. During the formation of primary sludge, there is minimal decomposition as it mainly involves the settling of solids. In contrast, a significant amount of decomposition occurs during the formation of activated sludge, as it is part of the secondary treatment process.

### Conclusion:
The incorrect statements are:
- **Statement (ii)**: "It possesses flocs of decomposer microbes." (Primary Sludge) vs. "It does not possess flocs of decomposer microbes." (Activated Sludge)
- **Statement (iv)**: "A lot of decomposition occurs during formation of primary sludge." vs. "Very little decomposition occurs during formation of activated sludge."

### Final Answer:
The incorrect statements are (ii) and (iv).

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