The least positive electron gain enthalpy is for

Options

A. He
B. Ne
C. Ar
D. Xe

Answer

To determine which inert gas has the least positive electron gain enthalpy, we need to analyze the properties of the noble gases. The electron gain enthalpy refers to the energy change when an electron is added to a neutral atom in the gas phase.

### Step-by-Step Solution:

1. **Identify the Noble Gases**: The noble gases are Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn).

2. **Understand Electron Gain Enthalpy**: Electron gain enthalpy is generally positive for noble gases because they have a complete valence shell and do not tend to gain electrons. However, the value can vary among the noble gases.

3. **Consider Atomic Size**: The atomic size of noble gases increases as you move down the group in the periodic table. This means Helium is the smallest, followed by Neon, Argon, Krypton, Xenon, and Radon.

4. **Relate Size to Electron Affinity**: Smaller atoms have a higher effective nuclear charge relative to their size, which can lead to a greater tendency to attract additional electrons. Therefore, Helium, being the smallest, will have the highest tendency to accept an electron, resulting in the least positive electron gain enthalpy.

5. **Evaluate the Options**: Since the question asks for the least positive electron gain enthalpy, we conclude that Helium (He) has the least positive value among the noble gases.

6. **Final Answer**: The least positive electron gain enthalpy is for Helium (He).