The incorrect statement among the following is

Options

A. The first ionization energy of Al is less than the first ionization energy of Mg
B. The second ionization energy of Mg is greater than the second ionization energy of Na
C. The first ionization energy of Na is less than the first ionization energy of Mg
D. The third ionization energy of Mg is greater than the third ionization energy of Al

Answer

To determine the incorrect statement among the given options regarding ionization energies, we will analyze each statement step by step.

### Step 1: Analyze the first statement
**Statement:** The first ionization energy of aluminium is less than the first ionization energy of magnesium.

- **Electronic Configurations:**
- Aluminium (Al): 1s² 2s² 2p⁶ 3s² 3p¹
- Magnesium (Mg): 1s² 2s² 2p⁶ 3s²

- **Analysis:**
- Aluminium has three electrons in its outer shell (3s² 3p¹), while magnesium has two (3s²).
- To remove one electron from aluminium (which has one electron in the 3p orbital), it requires less energy compared to removing one from magnesium, where the 3s orbital is fully filled.

- **Conclusion:** This statement is **correct**.

### Step 2: Analyze the second statement
**Statement:** The second ionization energy of magnesium is greater than the second ionization energy of sodium.

- **Electronic Configurations:**
- After losing one electron:
- Magnesium (Mg⁺): 1s² 2s² 2p⁶ 3s¹
- Sodium (Na⁺): 1s² 2s² 2p⁶

- **Analysis:**
- For magnesium, removing the second electron means removing the last electron from a partially filled 3s orbital.
- For sodium, removing the second electron means removing an electron from a full shell (2p⁶), which is more stable.

- **Conclusion:** The second ionization energy of magnesium is **less than** that of sodium. This statement is **incorrect**.

### Step 3: Analyze the third statement
**Statement:** The first ionization energy of sodium is less than the first ionization energy of magnesium.

- **Analysis:**
- Sodium has one electron in its outer shell (3s¹), while magnesium has two (3s²).
- It is easier to remove the single electron from sodium than to remove one from magnesium, which has a filled 3s orbital.

- **Conclusion:** This statement is **correct**.

### Step 4: Analyze the fourth statement
**Statement:** The third ionization energy of magnesium is greater than the third ionization energy of aluminium.

- **Electronic Configurations:**
- After losing two electrons:
- Magnesium (Mg²⁺): 1s² 2s² 2p⁶
- Aluminium (Al²⁺): 1s² 2s² 2p⁶ 3s¹

- **Analysis:**
- Magnesium has a full outer shell (noble gas configuration) after losing two electrons, while aluminium still has one electron in the 3s orbital.
- It requires more energy to remove an electron from a full shell compared to a partially filled one.

- **Conclusion:** This statement is **correct**.

### Final Conclusion
The incorrect statement among the options is the second statement: "The second ionization energy of magnesium is greater than the second ionization energy of sodium."

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