According to kinetic theory of gases:

Options

A. collisions are always elastic
B. heavier molecules transfer more momentum to the wall of the container
C. only a small number of molecules have very high velocity
D. between collisions, the molecules move in straight lines with constant velocities

Explanation

To solve the question according to the kinetic theory of gases, we need to analyze each of the given options based on the principles of the kinetic theory.

### Step-by-Step Solution:

1. **Understanding Elastic Collisions**:
- According to the kinetic theory of gases, gas molecules collide with each other and with the walls of the container. These collisions are perfectly elastic, meaning that there is no net loss of kinetic energy in the system.
- **Conclusion**: Option 1 is correct.

2. **Momentum Transfer**:
- The statement about heavier molecules transferring more momentum to the walls of the container is misleading. While heavier molecules can transfer more momentum due to their mass, this is not a postulate of the kinetic theory of gases. The theory primarily focuses on the behavior of gas molecules and their collisions rather than the specifics of momentum transfer based on mass.
- **Conclusion**: Option 2 is incorrect.

3. **Distribution of Molecular Speeds**:
- According to the Maxwell-Boltzmann distribution, not all gas molecules have the same speed. Most molecules have an average speed, and only a small number of molecules have very high or very low speeds. Therefore, this statement aligns with the kinetic theory.
- **Conclusion**: Option 3 is correct.

4. **Molecular Motion Between Collisions**:
- The kinetic theory states that gas molecules move in straight lines with constant velocity between collisions. When they collide with another molecule or the walls of the container, they change direction, but between these collisions, their motion is uniform.
- **Conclusion**: Option 4 is correct.

### Final Answer:
- The correct options according to the kinetic theory of gases are:
- Option 1: Collisions are always elastic.
- Option 3: Only a small number of molecules have very high velocity.
- Option 4: Between collisions, the molecules move in straight lines with constant velocity.