When longitudinal wave propagates through a medium, then the physical quantities _propagating in the direction of wave are

Options

A. Energy
B. Energy, momentum and mass
C. Energy and mass
D. Energy and momentum

Explanation

To solve the question, "When a longitudinal wave propagates through a medium, then the physical quantities propagating in the direction of the wave are?", we need to analyze the characteristics of longitudinal waves, specifically how they transmit energy, momentum, and mass.

### Step-by-Step Solution:

1. **Understanding Longitudinal Waves**:
- Longitudinal waves are waves in which the particle displacement is parallel to the direction of wave propagation. A common example of a longitudinal wave is sound.

2. **Energy Transfer**:
- In a longitudinal wave, energy is transferred through the vibrations of particles in the medium. When one particle vibrates, it collides with its neighboring particle, transferring energy to it. This process continues along the medium.

3. **Momentum Transfer**:
- Momentum is defined as the product of mass and velocity. In the case of longitudinal waves, while energy is transferred, the individual particles do not travel with the wave; they only oscillate around their equilibrium positions. Therefore, there is no net transfer of mass, and consequently, there is no net transfer of momentum in the direction of wave propagation.

4. **Mass Transfer**:
- In longitudinal waves, the particles of the medium do not move along with the wave. They only vibrate back and forth around their equilibrium positions. Thus, there is no mass transfer from one location to another in the direction of wave propagation.

5. **Conclusion**:
- The only physical quantity that propagates in the direction of the wave in a longitudinal wave is energy. Therefore, the correct answer to the question is that energy is the physical quantity propagating in the direction of the wave.

### Final Answer:
The physical quantity propagating in the direction of the wave in a longitudinal wave is **energy**.