The enzyme which has polymerising activity in `5' to 3'` direction but exonuclease activity in `3' to 5'` direction only is :-

Options

A. RNA polymerase III
B. DNA polymerase II
C. DNA polymerase I
D. All of these

Answer

To solve the question regarding the enzyme that has polymerizing activity in the 5' to 3' direction and exonuclease activity in the 3' to 5' direction, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Polymerizing Activity**:
- Polymerizing activity refers to the ability of an enzyme to synthesize long chains of nucleic acids (DNA or RNA). This activity is always in the 5' to 3' direction for all polymerases.

2. **Identify Exonuclease Activity**:
- Exonuclease activity involves the removal of nucleotides one at a time from the end of a polynucleotide chain. The specific activity mentioned in the question is 3' to 5' exonuclease activity, which is often associated with proofreading during DNA replication.

3. **Evaluate the Options**:
- **RNA Polymerase III**: This enzyme synthesizes RNA but does not have exonuclease activity. Therefore, it cannot be the answer.
- **DNA Polymerase I**: This enzyme has both 5' to 3' polymerizing activity and 3' to 5' exonuclease activity. It is involved in DNA repair and replication.
- **DNA Polymerase II**: Similar to DNA Polymerase I, it also has 5' to 3' polymerizing activity and 3' to 5' exonuclease activity.
- **All of These**: This option suggests that all the mentioned enzymes have the required activities, which is incorrect since RNA Polymerase III lacks exonuclease activity.

4. **Conclusion**:
- The enzymes that meet the criteria of having polymerizing activity in the 5' to 3' direction and exonuclease activity in the 3' to 5' direction are **DNA Polymerase I and DNA Polymerase II**.

### Final Answer:
The correct answer is **DNA Polymerase I and DNA Polymerase II**.