Which of the following statements is wrong?

Options

A. The first ionisationpotential of `Al` is less than the first ionisation potential of `Mg`.
B. The second ionisation potential of `Mg` is greater than the second ionisation potential of `Na`
C. The first ionisation potential of `Na` is less than the first ionsation potential of `Mg`.
D. The third ionisation potential of `Mg` is greater than the third ionisation potential of `Na`

Explanation

To determine which of the statements is wrong, we will analyze each statement step by step based on the principles of ionization potential and electronic configurations.

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

- **Electronic Configuration:**
- Aluminum (Al): 1s² 2s² 2p⁶ 3s² 3p¹
- Magnesium (Mg): 1s² 2s² 2p⁶ 3s²

- **Stability Consideration:**
- Magnesium has a completely filled 3s subshell, which is more stable compared to aluminum, which has an incompletely filled 3p subshell.

- **Conclusion:**
- Since magnesium has a more stable electronic configuration, its first ionization potential will be higher than that of aluminum. Therefore, this statement is **correct**.

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

- **Electronic Configuration of Ions:**
- Sodium ion (Na⁺): 1s² 2s² 2p⁶ (stable noble gas configuration)
- Magnesium ion (Mg⁺): 1s² 2s² 2p⁶ 3s¹

- **Stability Consideration:**
- Na⁺ has a stable noble gas configuration, while Mg⁺ is less stable due to the presence of an unfilled 3s subshell.

- **Conclusion:**
- Since Na⁺ is more stable, its second ionization potential will be higher than that of Mg. Therefore, this statement is **wrong**.

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

- **Electronic Configuration:**
- Sodium (Na): 1s² 2s² 2p⁶ 3s¹
- Magnesium (Mg): 1s² 2s² 2p⁶ 3s²

- **Stability Consideration:**
- Sodium has an unfilled 3s subshell, while magnesium has a filled 3s subshell, making magnesium more stable.

- **Conclusion:**
- Thus, the first ionization potential of sodium is indeed less than that of magnesium. This statement is **correct**.

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

- **Electronic Configuration of Ions:**
- Sodium ion (Na²⁺): 1s² 2s² 2p⁵
- Magnesium ion (Mg²⁺): 1s² 2s² 2p⁶ (noble gas configuration)

- **Stability Consideration:**
- Mg²⁺ has a stable noble gas configuration, while Na²⁺ does not.

- **Conclusion:**
- Therefore, the third ionization potential of magnesium is indeed greater than that of sodium. This statement is **correct**.

### Final Conclusion
After analyzing all statements, the wrong statement is:
**B. The second ionization potential of magnesium is higher than the second ionization potential of sodium.**