Which of the following assumptions is incorrect according to kinetic theory of gases ?

Options

A. Particles of a gas move in all possible directions in straight lines .
B. All the particles , at any particular time , have same speed and same kinetic energy .
C. There is no force of attraction between the particles of a gas at ordinary temperature and pressure .
D. The actual volume of the gas is negligible in comparison to the empty space between them .

Answer

To determine which assumption is incorrect according to the kinetic theory of gases, we will analyze the main assumptions of the theory step by step.

### Step 1: Understand the Assumptions of Kinetic Theory of Gases
The kinetic theory of gases is based on several key assumptions about the behavior of gas particles. These include:

1. **Particles are Tiny and Far Apart**: Gas particles are considered to be point masses with negligible volume compared to the volume of the container.
2. **No Intermolecular Forces**: There are no attractive or repulsive forces between the particles at ordinary temperatures and pressures.
3. **Continuous and Random Motion**: Gas particles are in constant motion and move in all directions.
4. **Straight-Line Motion**: Gas particles move in straight lines until they collide with another particle or the walls of the container.
5. **Kinetic Energy**: The average kinetic energy of gas particles is proportional to the temperature of the gas.
6. **Different Speeds and Kinetic Energies**: Not all particles have the same speed or kinetic energy; they vary due to differences in speed.

### Step 2: Analyze the Given Options
Now, let's evaluate the options provided in the question to identify which assumption is incorrect.

- **Option A**: "Particles of gas move in all possible directions in a straight line."
- This is correct according to the kinetic theory.

- **Option B**: "All the particles at any particular time have the same speed and same kinetic energy."
- This is incorrect. According to the kinetic theory, different particles have different speeds and kinetic energies.

- **Option C**: "There is no force of attraction between the particles of a gas at ordinary temperature and pressure."
- This is correct as per the assumptions of the kinetic theory.

- **Option D**: "The actual volume of gas is negligible in comparison to the empty space between them."
- This is also correct according to the kinetic theory.

### Conclusion
The incorrect assumption according to the kinetic theory of gases is **Option B**: "All the particles at any particular time have the same speed and same kinetic energy."