The main reason for deviation of gases from ideal behaviour is few assumptions of kinetic theory . These are
(i) there is no force of attraction between the molecules of a gas
(ii) volume of the molecules of a gas is negligibly small in comparison to the volume of the gas
(iii) particles of a gas are always in constant random motion .

Options

A. (i) and (ii)
B. (ii) and (iii)
C. (i) , (ii) and (iii)
D. (iii) only

Explanation

To determine the main reasons for the deviation of gases from ideal behavior based on the assumptions of the kinetic theory, we can analyze each of the statements provided in the question.

### Step-by-Step Solution:

1. **Identify the Assumptions of Kinetic Theory**:
- The kinetic theory of gases is based on several assumptions. The three statements given in the question are:
(i) There is no force of attraction between the molecules of a gas.
(ii) The volume of the molecules of a gas is negligibly small in comparison to the volume of the gas.
(iii) Particles of a gas are always in constant random motion.

2. **Evaluate Each Statement**:
- **Statement (i)**: "There is no force of attraction between the molecules of a gas."
- This statement is a fundamental assumption of the ideal gas law. In reality, gases do exhibit intermolecular forces, especially at high pressures and low temperatures. Therefore, this statement is not true in practical scenarios.

- **Statement (ii)**: "The volume of the molecules of a gas is negligibly small in comparison to the volume of the gas."
- This assumption holds true for ideal gases under normal conditions. However, at high pressures, the volume of gas molecules can no longer be considered negligible. Thus, this statement is also not entirely accurate in all conditions.

- **Statement (iii)**: "Particles of a gas are always in constant random motion."
- This statement is generally true and is a key aspect of the kinetic theory. However, it does not directly contribute to the deviation from ideal behavior. All gases exhibit random motion, whether they behave ideally or not.

3. **Conclusion**:
- The deviations from ideal gas behavior primarily arise from the failure of the first two assumptions under certain conditions (high pressure and low temperature). Therefore, the correct assumptions that lead to deviations are:
- (i) There is no force of attraction between the molecules of a gas (incorrect in real scenarios).
- (ii) The volume of the molecules of a gas is negligibly small in comparison to the volume of the gas (also incorrect under certain conditions).
- Statement (iii) does not affect the ideal behavior of gases.

4. **Final Answer**:
- The correct answer is that the first two statements are the main reasons for the deviation of gases from ideal behavior.