Which one of the following is not an assumption in the kinetic theory of gases?

Options

A. The volume occupied by the molecules of the gas in negligible
B. The force of attraction between the molecules is negligible
C. The collision between molecules are elastic
D. All molecules have same speed

Explanation

To determine which statement is not an assumption in the kinetic theory of gases, we need to analyze each option provided. The kinetic theory of gases is based on several key assumptions about the behavior of gas molecules. Let's go through the options step by step:

1. **Volume occupied by the molecules of the gas is negligible**:
- This is indeed an assumption of the kinetic theory. It assumes that the actual volume of the gas molecules is much smaller than the volume of the container they occupy. Thus, the volume of the molecules themselves can be ignored in calculations.

2. **The force of attraction between the molecules is negligible**:
- This is also a correct assumption in the kinetic theory. It assumes that gas molecules do not exert significant forces on each other except during collisions, meaning that intermolecular forces can be considered negligible.

3. **The collisions between the molecules are elastic**:
- This statement is true and is another assumption of the kinetic theory. It states that when gas molecules collide with each other or with the walls of the container, they do so in a way that conserves both momentum and kinetic energy.

4. **All molecules have the same speed**:
- This statement is incorrect in the context of the kinetic theory of gases. The theory actually assumes that gas molecules move at different speeds and that their speeds follow a distribution (Maxwell-Boltzmann distribution). Therefore, this is not an assumption of the kinetic theory.

Based on the analysis, the statement "All molecules have the same speed" is not an assumption in the kinetic theory of gases.

**Final Answer**: All molecules have the same speed (This is not an assumption in the kinetic theory of gases).

---