Which of the following postulate of kinetic theory of gas is responsible for deviation from ideal behaviour?

Options

A. kinetic energy of the gas molecules increase with increase in temperature
B. Collisions among the gas molecules are perfectly elastic
C. There is no forces of attraction or repulsion among gas molecules
D. Molecules in a gas follow zig-zag path

Answer

To determine which postulate of the kinetic theory of gases is responsible for the deviation from ideal behavior, we can analyze the given options step by step.

### Step 1: Understand the Kinetic Theory of Gases
The kinetic theory of gases is based on several postulates that describe the behavior of ideal gases. These postulates include:
1. Gas molecules are in constant random motion.
2. The volume of the gas molecules is negligible compared to the volume of the container.
3. There are no intermolecular forces of attraction or repulsion between gas molecules.
4. Collisions between gas molecules are perfectly elastic.

### Step 2: Identify the Postulates
From the options provided:
1. Kinetic energy of gas molecules.
2. Collisions among gas molecules are perfectly elastic.
3. There is no force of attraction or repulsion among gas molecules.

### Step 3: Analyze Each Postulate
- **Kinetic energy of gas molecules**: This postulate relates to the speed and energy of the molecules but does not directly address deviations from ideal behavior.
- **Collisions among gas molecules are perfectly elastic**: This postulate implies that energy is conserved during collisions, which is a characteristic of ideal gases. This does not contribute to deviations.
- **There is no force of attraction or repulsion among gas molecules**: This postulate is crucial because real gases do exhibit intermolecular forces, which leads to deviations from ideal behavior, especially under high pressure and low temperature conditions.

### Step 4: Conclusion
The postulate that is responsible for the deviation from ideal behavior is:
**Option 3: There is no force of attraction or repulsion among gas molecules.**

### Final Answer
The postulate responsible for deviation from ideal behavior is: **There is no force of attraction or repulsion among gas molecules.**

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