Whicn one fo the following has the lowest ionisation enthalpy ?

Options

A. `1s ^(2) 2s ^(2) 2p ^(6)`
B. `1s ^(2) 2s ^(2) 2p ^(6) 3s ^(1)`
C. `1s (2) 2s ^(2) 2p ^(5)`
D. `1s ^(2) 2s ^(2) 2p ^(3)`

Answer

To determine which of the given elements has the lowest ionization enthalpy, we need to analyze the electron configurations of the elements provided and understand the concept of ionization enthalpy.

### Step-by-Step Solution:

1. **Understand Ionization Enthalpy**:
- Ionization enthalpy (or ionization energy) is the amount of energy required to remove the outermost electron from an isolated gaseous atom. The lower the ionization energy, the easier it is to remove an electron.

2. **Identify the Electron Configurations**:
- The question provides four options with their electron configurations:
- **Option 1**: 1s² 2s² 2p⁶ (Atomic number = 10, Neon)
- **Option 2**: 1s² 2s² 2p⁶ 3s¹ (Atomic number = 11, Sodium)
- **Option 3**: 1s² 2s² 2p⁵ (Atomic number = 9, Fluorine)
- **Option 4**: 1s² 2s² 2p³ (Atomic number = 7, Nitrogen)

3. **Analyze Stability of Electron Configurations**:
- Atoms with a full outer shell (like Neon) or half-filled subshells (like Nitrogen) are more stable and require more energy to remove an electron.
- Sodium has one electron in its outermost shell (3s¹), making it easier to remove compared to the others.
- Fluorine has 7 electrons in its outer shell (2p⁵) and tends to gain an electron rather than lose one, indicating higher ionization energy.

4. **Compare the Elements**:
- **Neon (Option 1)**: Full outer shell (high ionization energy).
- **Sodium (Option 2)**: One electron in the outer shell (low ionization energy).
- **Fluorine (Option 3)**: Almost full outer shell (high ionization energy).
- **Nitrogen (Option 4)**: Half-filled subshell (moderate ionization energy).

5. **Conclusion**:
- Among the options, Sodium (Option 2) has the lowest ionization enthalpy because it has only one electron in its outermost shell, which can be removed easily.

### Final Answer:
**Sodium (Option 2) has the lowest ionization enthalpy.**