The energy required to pull the most loosely bound electron form an atom is known as ionizatino potential it is expressed in electron volts. The value of ionization potntial depends on three factors: (i) the charge on the nucleus (ii) the atomic radius and (iii) the screening effect of inner electron shells.
Q. Incorrect order of ionisation energy is:

Options

A. `Pb(I.E.) gt Sn(I.E.)`
B. `Na^(+)(I.E.) gt Mg^(+) (I.E.)`
C. `Li^(+)(I.E.) lt O^(+) (I.E.)`
D. `Be^(+) (I.E.) lt C^(+) (I.E.)`

Answer

To determine the incorrect order of ionization energy among the given options, we will analyze each option based on the factors that influence ionization energy: the charge on the nucleus, atomic radius, and the screening effect of inner electron shells.

### Step-by-Step Solution:

1. **Understanding Ionization Energy**:
- Ionization energy is the energy required to remove the most loosely bound electron from an atom. It generally increases with increasing nuclear charge and decreases with increasing atomic radius and screening effect.

2. **Analyzing Option A**:
- **Statement**: Ionization energy of Pb (Lead) is greater than Sn (Tin).
- **Analysis**: Both Pb and Sn are in Group 14. As we move down the group, ionization energy decreases due to increased atomic radius and shielding effect. However, Pb has a higher ionization energy than Sn due to the inert pair effect.
- **Conclusion**: This statement is correct.

3. **Analyzing Option B**:
- **Statement**: Ionization energy of Na⁺ (Sodium ion) is greater than Mg⁺ (Magnesium ion).
- **Analysis**: Both Na⁺ and Mg⁺ are isoelectronic with Ne (noble gas configuration). However, Na⁺ has a lower effective nuclear charge compared to Mg⁺, which means it would require less energy to remove an electron from Na⁺ than from Mg⁺.
- **Conclusion**: This statement is incorrect.

4. **Analyzing Option C**:
- **Statement**: Ionization energy of Li⁺ (Lithium ion) is less than O⁺ (Oxygen ion).
- **Analysis**: Li⁺ has a noble gas configuration (1s²), while O⁺ has a configuration of 1s² 2s² 2p³. Removing an electron from O⁺ requires more energy than from Li⁺ due to higher effective nuclear charge in O⁺.
- **Conclusion**: This statement is correct.

5. **Analyzing Option D**:
- **Statement**: Ionization energy of Be⁺ (Beryllium ion) is less than C⁺ (Carbon ion).
- **Analysis**: Be⁺ has a configuration of 1s² 2s¹, and C⁺ has a configuration of 1s² 2s² 2p¹. Removing an electron from Be⁺ requires less energy because it achieves a noble gas configuration after losing one electron.
- **Conclusion**: This statement is correct.

### Final Answer:
The incorrect order of ionization energy is found in **Option B**: Ionization energy of Na⁺ is greater than Mg⁺.