Cyanobacteria differes from bacteria in many respects in :
`1`. Complete absence of flagella
`2`. Presence of both `PS I`, `PS II`
`3`. Photosynthesis is anoxygenic
`4`. Carotenes and Chlorophylls are present

Options

A. `1,2,3` are correct
B. `2,3` are correct
C. `2,3,4` are correct
D. `1,2,4` are correct

Answer

To solve the question regarding how cyanobacteria differ from bacteria, we will analyze each of the provided statements one by one.

### Step-by-Step Solution:

1. **Statement 1: Complete absence of flagella**
- Cyanobacteria are known to lack flagella, which are structures used for movement in many bacteria. This statement is **true**.

2. **Statement 2: Presence of both PS I and PS II**
- Cyanobacteria contain both Photosystem I (PS I) and Photosystem II (PS II), which are essential for oxygenic photosynthesis. This statement is also **true**.

3. **Statement 3: Photosynthesis is anoxygenic**
- This statement is **false**. Cyanobacteria perform oxygenic photosynthesis, which means they produce oxygen as a byproduct. In contrast, anoxygenic photosynthesis occurs in some other bacteria, where oxygen is not produced.

4. **Statement 4: Carotenes and chlorophylls are present**
- Cyanobacteria contain chlorophyll a and various carotenoids, which are pigments that assist in photosynthesis. This statement is **true**.

### Conclusion:
From the analysis:
- Statements 1, 2, and 4 are true.
- Statement 3 is false.

Thus, the correct answer is that cyanobacteria differ from bacteria in statements **1, 2, and 4**.

### Final Answer:
Cyanobacteria differ from bacteria in:
- 1. Complete absence of flagella (True)
- 2. Presence of both PS I and PS II (True)
- 3. Photosynthesis is anoxygenic (False)
- 4. Carotenes and chlorophylls are present (True)

**Correct options: 1, 2, 4**