Which of the following were called permanent gases ?
(i) `H_(2)` , (ii) `O_(2)`
(iii) `N_(2)` , (iv) `CH_(4)`

Options

A. `(i),(ii),(iii)`
B. `(i),(ii),(iii),(iv)`
C. `(ii),(iii),(iv)`
D. `(i),(ii)`

Explanation

To determine which of the given gases are classified as permanent gases, we need to understand the definition of permanent gases and analyze each option accordingly.

### Step-by-Step Solution:

1. **Understanding Permanent Gases**:
- Permanent gases are those gases that do not liquefy at room temperature, regardless of the pressure applied. This means that even under high pressure, they remain in the gaseous state.

2. **Analyzing Each Gas**:
- **(i) H₂ (Hydrogen)**: Hydrogen can be liquefied under sufficient pressure and low temperature. Therefore, it is not considered a permanent gas.
- **(ii) O₂ (Oxygen)**: Oxygen can also be liquefied under certain conditions. Thus, it is not a permanent gas.
- **(iii) N₂ (Nitrogen)**: Nitrogen is known to remain in the gaseous state under normal conditions and does not liquefy easily, making it a permanent gas.
- **(iv) CH₄ (Methane)**: Methane can be liquefied under specific conditions, but it is often considered a permanent gas in many contexts because it requires significant pressure and low temperature to liquefy.

3. **Conclusion**:
- From the analysis, the gases that can be classified as permanent gases are **N₂ (Nitrogen)** and **CH₄ (Methane)**. However, since the definition of permanent gases can vary, in some contexts, only N₂ is strictly considered a permanent gas.

### Final Answer:
The permanent gases among the options provided are **(iii) N₂** and **(iv) CH₄**.

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