Which of the following gases always show positive deviation from ideal behaviour with increase in pressure ?

Options

A. `NH_(3)`
B. `CO_(2)`
C. `H_(2)`
D. CO

Explanation

To determine which gases always show positive deviation from ideal behavior with an increase in pressure, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Ideal Gas Behavior**:
The ideal gas equation is given by \( PV = nRT \), where \( P \) is pressure, \( V \) is volume, \( n \) is the number of moles, \( R \) is the gas constant, and \( T \) is temperature. Under ideal conditions, gases behave according to this equation.

**Hint**: Recall the ideal gas law and its assumptions about gas behavior.

2. **Introduce Compressibility Factor (Z)**:
The compressibility factor \( Z \) is defined as \( Z = \frac{PV}{RT} \). This factor helps us understand how real gases deviate from ideal behavior.

**Hint**: Remember that \( Z \) indicates how much a real gas deviates from ideal behavior.

3. **Determine Conditions for Positive Deviation**:
If \( Z > 1 \), the gas shows positive deviation from ideal behavior. This means that the gas occupies more volume than predicted by the ideal gas law under certain conditions.

**Hint**: Focus on the relationship between the compressibility factor and deviations from ideal behavior.

4. **Analyze the Effect of Increasing Pressure**:
When pressure increases, the volume of the gas tends to decrease. For certain gases, such as hydrogen (H2) and helium (He), the intermolecular forces become significant, leading to a situation where \( Z \) remains greater than 1 even as pressure increases.

**Hint**: Consider how the behavior of specific gases changes with pressure and volume.

5. **Identify Gases with Consistent Positive Deviation**:
Among the common gases, hydrogen (H2) and helium (He) consistently show positive deviation from ideal behavior with increasing pressure due to their low molecular weights and weak intermolecular forces.

**Hint**: Think about the properties of light gases and their behavior under high pressure.

6. **Conclusion**:
Based on the analysis, the gas that always shows positive deviation from ideal behavior with an increase in pressure is hydrogen (H2).

**Final Answer**: The gas that always shows positive deviation from ideal behavior with an increase in pressure is **H2 (hydrogen gas)**.