Assertion (A): The muscular walls of ventricles are thicker than auricles.
Reason (R): This helps in preventing the back flow of blood.

Options

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

Explanation

**Step-by-Step Solution:**

1. **Understanding the Assertion (A)**: The assertion states that "The muscular walls of ventricles are thicker than auricles." This is true because the ventricles are responsible for pumping blood to the entire body (left ventricle) or to the lungs (right ventricle), which requires more muscular strength.

2. **Understanding the Reason (R)**: The reason given is "This helps in preventing the back flow of blood." This statement is misleading. While the thickness of the ventricular walls is important for pumping blood effectively, the prevention of backflow is primarily managed by the heart valves (such as the mitral and tricuspid valves) rather than the thickness of the ventricular walls.

3. **Evaluating the Statements**:
- The assertion is true (the walls of the ventricles are indeed thicker).
- The reason is false (the thickness does not prevent backflow; valves do that).

4. **Conclusion**: Based on the evaluation, the correct relationship is that the assertion is true, but the reason is false. Therefore, the answer is that the assertion is true and the reason is false.

**Final Answer**: Assertion (A) is true, and Reason (R) is false.

---