Mark the wrong statement

Options

A. Sliding of molecular layer is much easier than compression or expansion.
B. Reciprocal of bulk modulus of elasticiy is called compressibility
C. It is difficult to twist a long rod as compared to small rod.
D. Hollow shaft is much stronger than a solid rod of same length and same mass.

Explanation

To solve the question of identifying the wrong statement among the given options, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze Option A**:
- Statement: "Sliding of molecular layer is much easier than compression or expansion."
- Explanation: This statement is true. In materials, the sliding of molecular layers (shear deformation) typically requires less force compared to the forces needed for compression or expansion (bulk deformation).

2. **Analyze Option B**:
- Statement: "The reciprocal of bulk modulus of elasticity is called compressibility."
- Explanation: This statement is also true. The bulk modulus (K) is defined as the ratio of pressure increase to the resulting decrease in volume. Compressibility (k) is indeed the reciprocal of bulk modulus, expressed as \( k = \frac{1}{K} \).

3. **Analyze Option C**:
- Statement: "It is difficult to twist a long rod as compared to a small rod."
- Explanation: This statement is false. The angle of twist (φ) is inversely proportional to the length (L) of the rod. Therefore, a longer rod will twist less for the same applied torque compared to a shorter rod. Thus, it is easier to twist a long rod than a short one.

4. **Analyze Option D**:
- Statement: "A hollow shaft is much stronger than a solid rod of the same length and the same mass."
- Explanation: This statement is true. A hollow shaft can withstand greater torsional stress compared to a solid rod of the same mass and length due to its geometry, which allows for better distribution of stress.

### Conclusion:
- The wrong statement is **Option C**.

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