The third ionization enthalpy is maximum for

Options

A. nitrogen
B. phosphorus
C. aluminium
D. boron

Answer

To determine which element has the maximum third ionization enthalpy, we need to analyze the electronic configurations of the given elements and understand the concept of ionization enthalpy.

### Step-by-Step Solution:

1. **Understand Ionization Enthalpy**:
- Ionization enthalpy is the energy required to remove an electron from an atom in the gaseous state. The third ionization enthalpy refers to the energy required to remove the third electron.

2. **Identify the Elements**:
- The elements mentioned in the video are:
- Nitrogen (N) - Atomic number 7: Electronic configuration: 1s² 2s² 2p³
- Phosphorus (P) - Atomic number 15: Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p³
- Aluminum (Al) - Atomic number 13: Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p¹
- Boron (B) - Atomic number 5: Electronic configuration: 1s² 2s² 2p¹

3. **Remove Electrons for Third Ionization**:
- For each element, we analyze what remains after removing two electrons (to reach the state before the third ionization):
- **Nitrogen**: After removing 2 electrons, we have 2p¹ remaining.
- **Phosphorus**: After removing 2 electrons, we have 3p¹ remaining.
- **Aluminum**: After removing 2 electrons, we have 3s¹ remaining.
- **Boron**: After removing 2 electrons, we have 2p⁰ remaining (which is stable).

4. **Evaluate the Remaining Configuration**:
- The remaining configurations after the second ionization are:
- Nitrogen: 2p¹
- Phosphorus: 3p¹
- Aluminum: 3s¹
- Boron: 2s² (after removing 2p electrons, boron is left with a full inner shell, making it stable).

5. **Consider the Nuclear Charge and Distance**:
- The third ionization enthalpy will be highest for the element where the remaining electron is held most tightly by the nucleus.
- Boron, with its remaining electrons in the 1s² and 2s² orbitals, experiences a strong effective nuclear charge due to its proximity to the nucleus. Thus, it requires a large amount of energy to remove the third electron.

6. **Conclusion**:
- Therefore, the element with the maximum third ionization enthalpy is **Boron (B)**.

### Final Answer:
The third ionization enthalpy is maximum for **Boron (B)**.