Assertion`:` In fishes single circulation occur
Reason `:` Fishes have a 2-chambered hearts with an atrium and a ventricle.

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 "In fishes, single circulation occurs." This means that the blood flows through the heart only once during each complete circuit of the body. In fishes, blood is pumped from the heart to the gills for oxygenation and then directly to the rest of the body.

2. **Understanding the Reason**: The reason provided is that "Fishes have a 2-chambered heart with an atrium and a ventricle." This is a factual statement about the anatomy of fish hearts. A 2-chambered heart consists of one atrium and one ventricle, which is sufficient for the single circulation system.

3. **Explaining the Circulation Process**: In fishes, the circulation process starts with deoxygenated blood returning to the heart. The heart pumps this blood to the gills, where carbon dioxide is expelled and oxygen is absorbed. The oxygenated blood then travels to the rest of the body, where it delivers oxygen to tissues and collects carbon dioxide, returning to the heart to repeat the cycle.

4. **Evaluating the Relationship**: The reason (the structure of the fish heart) explains why the assertion (single circulation) is true. The presence of a 2-chambered heart is directly related to the single circulation system seen in fishes.

5. **Conclusion**: Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the correct answer is that both the assertion and reason are true and the reason is the correct explanation for the assertion.

**Final Answer**: Both assertion and reason are true, and the reason is the correct explanation for the assertion.

---