Assertion :- DNA replication is energetically a very expensive process.
Reason : Unwinding of DNA strands is an active process, while pairing of bases is a passive process.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are true but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are false.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "DNA replication is energetically a very expensive process."
- This is true because DNA replication requires a significant amount of energy, primarily in the form of ATP. Various enzymes and proteins are necessary for the process, all of which require energy to function.

2. **Understanding the Reason**:
- The reason provided states that "Unwinding of DNA strands is an active process, while pairing of bases is a passive process."
- This statement is false. The unwinding of DNA strands is actually a passive process facilitated by enzymes such as helicase and topoisomerase, which do not require additional energy input to unwind the DNA.

3. **Analyzing the Relationship**:
- The assertion is true, but the reason is false. Therefore, the reason does not correctly explain the assertion.

4. **Choosing the Correct Option**:
- Given the analysis, we conclude that the correct answer is:
- **Option C**: Assertion is true, and the reason is false.