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 required 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 differences between primary sludge and activated sludge, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Understanding Primary Sludge and Activated Sludge**:
- Primary sludge is formed during the primary sewage treatment process, which involves the physical removal of solids from wastewater.
- Activated sludge is formed during secondary sewage treatment, which involves biological processes to further treat the wastewater.

2. **Analyzing the Statements**:
- **Statement (i)**: "It is sludge formed during primary sewage treatment" (Primary Sludge) vs. "It is sludge formed during secondary sewage treatment" (Activated Sludge).
- This statement is **correct**. Primary sludge is indeed formed during primary sewage treatment, and activated sludge is formed during secondary sewage treatment.

- **Statement (ii)**: "It possesses flocs of decomposer microbes" (Activated Sludge) vs. "It does not possess flocs of decomposer microbes" (Primary Sludge).
- This statement is **incorrect**. Activated sludge contains flocs of decomposer microbes, while primary sludge does not contain these flocs.

- **Statement (iii)**: "It does not require aeration" (Primary Sludge) vs. "Formation of activated sludge required aeration" (Activated Sludge).
- This statement is **correct**. Primary sludge does not require aeration as it is treated anaerobically, while activated sludge formation requires aeration to support microbial activity.

- **Statement (iv)**: "A lot of decomposition occurs during formation of primary sludge" (Primary Sludge) vs. "Very little decomposition occurs during formation of activated sludge" (Activated Sludge).
- This statement is **incorrect**. In fact, very little decomposition occurs during the formation of primary sludge, while a lot of decomposition occurs during the formation of activated sludge.

3. **Identifying Incorrect Statements**:
- From the analysis, we find that:
- Statement (ii) is incorrect.
- Statement (iv) is also incorrect.

4. **Selecting the Incorrect Options**:
- Based on the incorrect statements identified:
- **Option A**: Incorrect (1st is correct).
- **Option B**: Correct (2nd and 4th are incorrect).
- **Option C**: Incorrect (1st is correct).
- **Option D**: Incorrect (3rd is correct).

Thus, the correct answer is **Option B**: "2nd and 4th are incorrect."