Assertion: Helium shows only positive deviations from ideal behaviour.
Reason: Helium is an inert gas.

Options

A. If both assertion and reason are correct and reason is correct explanation for assertion
B. If both assertion and reason are correct and reason is not correct explanation for assertion
C. If assertion is correct but reason is incorrect
D. If assertion and reason are both incorreect.

Explanation

To solve the question regarding the assertion and reason about helium's behavior as a gas, we will analyze both statements step by step.

### Step 1: Understand the Assertion
The assertion states that "Helium shows only positive deviations from ideal behavior."
- **Explanation**: In the context of gas behavior, positive deviation from ideal behavior means that the gas behaves less ideally than predicted by the ideal gas law. This typically occurs when the actual pressure of the gas is higher than what would be expected under ideal conditions.

### Step 2: Understand the Reason
The reason states that "Helium is an inert gas."
- **Explanation**: Helium is classified as a noble gas, which means it has a complete valence shell and does not readily react with other elements. This lack of interaction leads to very weak intermolecular forces between helium atoms.

### Step 3: Connect the Assertion and Reason
- Since helium is an inert gas, it has negligible intermolecular attractions. This means that when helium is in a gaseous state, it does not experience the attractive forces that would typically cause a gas to deviate negatively from ideal behavior. Instead, the lack of attraction leads to a positive deviation, as the gas molecules are more likely to behave independently of one another.

### Step 4: Conclusion
Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the answer to the question is that both the assertion and reason are true, and the reason is the correct explanation for the assertion.

### Final Answer
The correct option is A: Both the assertion and reason are true, and the reason is the correct explanation for the assertion.

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