Ammong the following, the element having highest ionization enthalpy as positive electron gain enthalpy is

Options

A. H
B. F
C. He
D. Na

Answer

To determine which element has the highest ionization enthalpy and positive electron gain enthalpy among hydrogen, fluorine, helium, and sodium, we can follow these steps:

### Step 1: Understand Ionization Enthalpy
Ionization enthalpy is the energy required to remove an electron from an atom in its gaseous state. Generally, the ionization enthalpy increases across a period and decreases down a group in the periodic table.

### Step 2: Understand Electron Gain Enthalpy
Electron gain enthalpy is the energy change when an electron is added to a neutral atom in the gaseous state. A positive electron gain enthalpy indicates that energy is required to add an electron, which typically occurs in elements that are less likely to gain electrons.

### Step 3: Analyze the Given Elements
1. **Hydrogen (H)**: Electron configuration is 1s¹. It has a relatively low ionization enthalpy because it has only one electron.
2. **Fluorine (F)**: Electron configuration is 1s² 2s² 2p⁵. It has a high ionization enthalpy due to its high electronegativity and the presence of unpaired electrons.
3. **Helium (He)**: Electron configuration is 1s². Helium has a complete outer shell, making it very stable and requiring a significant amount of energy to remove an electron, resulting in the highest ionization enthalpy among the given elements.
4. **Sodium (Na)**: Electron configuration is 1s² 2s² 2p⁶ 3s¹. Sodium has a low ionization enthalpy as it has one electron in its outermost shell which is relatively easy to remove.

### Step 4: Compare Ionization Enthalpies
From the analysis:
- Helium has the highest ionization enthalpy due to its stable electron configuration (1s²).
- Fluorine has a high ionization enthalpy as well, but not as high as helium.
- Hydrogen and sodium have lower ionization enthalpies compared to helium and fluorine.

### Step 5: Compare Electron Gain Enthalpies
- Helium has a positive electron gain enthalpy because it does not readily accept an electron due to its full outer shell.
- Fluorine has a negative electron gain enthalpy, indicating that it readily accepts an electron.
- Hydrogen has a positive electron gain enthalpy but is less than that of helium.
- Sodium also has a positive electron gain enthalpy but is less than that of helium.

### Conclusion
Based on the analysis, the element with the highest ionization enthalpy and positive electron gain enthalpy is **Helium (He)**.

### Final Answer
**Helium (He)**

---