Assertion : `O_(2)` easily diffuses from alveoli to tissues and `CO_(2)` from tissue to alveoli.
Reason : Alveoli is 2-celled thick and capillaries are thin walled.

Options

A. Both A and R are true and R is the correct explanation of A.
B. Both A and R are true but Ris not correct explanation of A
C. A is true but R is false
D. A and R are false

Answer

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

### Step 1: Analyze the Assertion
The assertion states: "O₂ easily diffuses from alveoli to tissues and CO₂ from tissues to alveoli."

- This statement is true. Oxygen (O₂) diffuses from the alveoli (where it is present at a higher concentration) into the blood in the capillaries and then from the blood to the tissues (where the concentration is lower). Conversely, carbon dioxide (CO₂) diffuses from the tissues (where it is produced and present at a higher concentration) into the blood and then from the blood to the alveoli (where the concentration is lower).

### Step 2: Analyze the Reason
The reason states: "Alveoli is 2-celled thick and capillaries are thin-walled."

- This statement is false. The alveoli are not two-celled thick; they are actually composed of a single layer of epithelial cells (simple squamous epithelium), which makes them very thin. Additionally, capillaries are also thin-walled, allowing for efficient gas exchange. Therefore, the reason does not accurately describe the structure of the alveoli.

### Step 3: Conclusion
- Since the assertion is true and the reason is false, we conclude that the assertion is correct, but the reason is not a valid explanation for the assertion.

### Final Answer
The assertion is true, and the reason is false.