Which one of the following is not an assumption in the kinetic theory of gases? a) The volume occupied by the molecules of the gas is negligible. b) The force of attraction between the molecules is negligible. c) The collision between the molecules are elastic. d) All molecules have same speed.

Options

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

Explanation

To solve the question, we need to analyze the assumptions of the kinetic theory of gases and identify which one is not an assumption.

### Step-by-Step Solution:

1. **Understanding the Kinetic Theory of Gases**:
The kinetic theory of gases is based on several key assumptions about the behavior of gas molecules.

2. **Assumption A**:
- "The volume occupied by the molecules of the gas is negligible."
- This assumption is correct. In the kinetic theory, gas molecules are considered to be point particles with no volume.

3. **Assumption B**:
- "The force of attraction between the molecules is negligible."
- This assumption is also correct. The kinetic theory assumes that there are no significant attractive or repulsive forces between gas molecules.

4. **Assumption C**:
- "The collisions between the molecules are elastic."
- This assumption is correct as well. In the kinetic theory, it is assumed that when gas molecules collide, they do so elastically, meaning that kinetic energy is conserved.

5. **Assumption D**:
- "All molecules have the same speed."
- This assumption is **not correct**. In reality, gas molecules have a distribution of speeds, and it is a fundamental assumption of the kinetic theory that different molecules can have different speeds.

6. **Conclusion**:
- The assumption that "all molecules have the same speed" is not an assumption in the kinetic theory of gases. Therefore, the correct answer is option D.

### Final Answer:
**D) All molecules have the same speed.**

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