Which of the following statement about `DNA` is not correct ?

Options

A. It has a double helix structure
B. It undergoes replication
C. The two strands in a `DNA` molecule are exactly similar
D. It contains the 2-deoxyribose pentose sugar.

Answer

To determine which statement about DNA is not correct, we will analyze each statement provided in the question.

### Step-by-Step Solution:

1. **Understanding DNA Structure**:
- DNA stands for deoxyribonucleic acid. It consists of a sugar (2-deoxyribose), phosphate group, and nitrogenous bases.

2. **Identifying the Statements**:
- We need to evaluate the following statements about DNA:
1. It has a double helix structure.
2. It undergoes replication.
3. The two strands in a DNA molecule are exactly similar.
4. It contains 2-deoxy sugar.

3. **Evaluating Each Statement**:
- **Statement 1**: "It has a double helix structure."
- This statement is correct. DNA is known for its double helical structure.

- **Statement 2**: "It undergoes replication."
- This statement is also correct. DNA replicates to produce identical copies during cell division.

- **Statement 3**: "The two strands in a DNA molecule are exactly similar."
- This statement is incorrect. The two strands of DNA are complementary, not identical. For example, if one strand has the sequence ATCG, the complementary strand will have TAGC.

- **Statement 4**: "It contains 2-deoxy sugar."
- This statement is correct. The sugar in DNA is indeed 2-deoxyribose.

4. **Conclusion**:
- The statement that is not correct is: "The two strands in a DNA molecule are exactly similar." This is the answer to the question.

### Final Answer:
The statement about DNA that is not correct is: **"The two strands in a DNA molecule are exactly similar."**