Assertion : A hollow shaft is found to be stronger than a solid shaft made of same material.
Reason : The torque required to produce a given twist in hollow cylinder is greater than that required to twist a solid cylinder of same size and material.

Answer

To analyze the assertion and reason provided, we will break down the statements step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "A hollow shaft is found to be stronger than a solid shaft made of the same material."
- To understand this, we need to consider the distribution of material in both shafts. A hollow shaft has material distributed away from the center, which can enhance its strength under torsional loads.

2. **Understanding the Reason**:
- The reason states, "The torque required to produce a given twist in a hollow cylinder is greater than that required to twist a solid cylinder of the same size and material."
- Torque (τ) is defined as τ = r × F, where r is the radius and F is the force applied. For a hollow cylinder, the effective radius where the material resists twisting is greater than that of a solid cylinder, which means that for the same material and dimensions, the hollow cylinder can withstand more torque before failing.

3. **Comparing the Strength**:
- When comparing the strength of both shafts, we can analyze their polar moment of inertia (J). The polar moment of inertia for a hollow shaft is greater than that of a solid shaft for the same outer diameter, which contributes to its ability to resist twisting.
- Therefore, under the same loading conditions, the hollow shaft can carry more load before yielding, making it stronger.

4. **Conclusion**:
- Both the assertion and the reason are correct. The hollow shaft is indeed stronger than a solid shaft made of the same material, and the reason provided accurately explains why the torque required to twist a hollow cylinder is greater than that for a solid cylinder of the same size and material.

### Final Statement:
- **Assertion**: True
- **Reason**: True
- Both statements are correct, and the reason correctly explains the assertion.