Which one is correct answer for plasmid
(i) It can be readily isolated from cells
(ii) It possesses a single recognition site for one restriction enzyme
(iii) It should have high molecular weight
(iv) Plasmids and bacteriophages have the ability to replicate within bacteria

Options

A. i, ii, iv
B. i, ii, iii, iv
C. ii, iii, iv
D. i, ii, iii

Answer

To determine which statement about plasmids is correct, we will analyze each option provided in the question.

1. **Understanding Plasmids**:
- Plasmids are small, circular, double-stranded DNA molecules that are separate from chromosomal DNA and can replicate independently within bacterial cells. They often carry genes that provide bacteria with genetic advantages, such as antibiotic resistance.

2. **Evaluating Each Statement**:
- **(i) It can be readily isolated from cells**:
- This statement is correct. Plasmids can be easily extracted from bacterial cells using plasmid isolation techniques, which involve breaking open the cells and separating the plasmid DNA from chromosomal DNA and other cellular components.

- **(ii) It possesses a single recognition site for one restriction enzyme**:
- This statement is also correct. Many plasmids are designed to have a single recognition site for a specific restriction enzyme, which allows for the insertion of foreign DNA at that site during cloning procedures.

- **(iii) It should have high molecular weight**:
- This statement is incorrect. Plasmids are typically of low molecular weight compared to chromosomal DNA. They are designed to be small to facilitate easy manipulation and transfer.

- **(iv) Plasmids and bacteriophages have the ability to replicate within bacteria**:
- This statement is correct. Both plasmids and bacteriophages can replicate within bacterial cells. Plasmids have autonomously replicating sequences (ARS) that allow them to replicate independently, while bacteriophages can hijack the bacterial machinery to replicate themselves.

3. **Conclusion**:
- The correct statements about plasmids are (i), (ii), and (iv). Therefore, the answer to the question is that options (i), (ii), and (iv) are correct regarding plasmids.

### Final Answer:
The correct statements about plasmids are (i), (ii), and (iv).