Which of the following has the highest negative electron gain entahlpy ?

Options

A. `F^(-)`
B. `O^(-)`
C. `Na^(+)`
D. `Mg^(2+)`

Answer

To determine which of the given options has the highest negative electron gain enthalpy, we will analyze each option step by step.

### Step 1: Understand Electron Gain Enthalpy
Electron gain enthalpy is defined as the energy released when an electron is added to an isolated gaseous atom. A more negative value indicates a greater tendency to gain an electron.

### Step 2: Analyze Each Option
We have four options to analyze: Fluoride ion (F⁻), Oxygen ion (O²⁻), Sodium ion (Na⁺), and Magnesium ion (Mg²⁺).

1. **Fluoride Ion (F⁻)**:
- Fluorine (F) has an atomic number of 9, meaning it has 9 electrons.
- The fluoride ion (F⁻) has gained one extra electron, resulting in a total of 10 electrons.
- This configuration is stable as it achieves the noble gas configuration of Neon.

2. **Oxygen Ion (O²⁻)**:
- Oxygen (O) has an atomic number of 8, meaning it has 8 electrons.
- The oxide ion (O²⁻) has gained two extra electrons, resulting in a total of 10 electrons.
- This also achieves a stable noble gas configuration.

3. **Sodium Ion (Na⁺)**:
- Sodium (Na) has an atomic number of 11, meaning it has 11 electrons.
- The sodium ion (Na⁺) has lost one electron, resulting in a total of 10 electrons.
- This configuration is stable as it achieves the noble gas configuration of Neon.

4. **Magnesium Ion (Mg²⁺)**:
- Magnesium (Mg) has an atomic number of 12, meaning it has 12 electrons.
- The magnesium ion (Mg²⁺) has lost two electrons, resulting in a total of 10 electrons.
- This configuration is also stable as it achieves the noble gas configuration.

### Step 3: Determine Stability and Electron Affinity
- Fluoride ion (F⁻), Sodium ion (Na⁺), and Magnesium ion (Mg²⁺) all have stable configurations and are less likely to gain an electron.
- The oxide ion (O²⁻), however, has a less stable configuration compared to the others and can easily accept an electron due to its incomplete outer shell.

### Step 4: Conclusion
Since O²⁻ can accept an electron more readily than the other options, it has the highest negative electron gain enthalpy. Therefore, the correct answer is:

**Answer: Option 2 (O²⁻)**

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