Assertion: Extranuclear chromosomes are present in mitochondria and plastids.
Reason: They are prochromosomes or organelle chromosomes

Options

A. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
B. If both Assertion and Reason are true and the Reason is not the correct explanation of the Assertion.
C. If Assertion is true but the Reason is false.
D. If both Assertion and Reason are false.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Extranuclear chromosomes are present in mitochondria and plastids."
- Extranuclear chromosomes refer to DNA that is located outside the nucleus. In eukaryotic cells, this type of DNA is indeed found in mitochondria and plastids (such as chloroplasts). Therefore, this assertion is **true**.

2. **Understanding the Reason**:
- The reason states that "They are prochromosomes or organelle chromosomes."
- The term "prochromosomes" refers to a structure found in prokaryotes, which is not applicable to the DNA found in mitochondria and plastids. Instead, the DNA in these organelles is often referred to as organelle DNA or mitochondrial DNA (mtDNA) and plastid DNA (cpDNA). Therefore, this reason is **false**.

3. **Conclusion**:
- Since the assertion is true and the reason is false, the correct answer is that the assertion is true but the reason is false.

### Final Answer:
The correct option is **C**: "Assertion is true but reason is false."

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