How many electrons are in the n = 3 shell of a magnesium ion (Mg²⁺)?

• A. 8
• B. 0
• C. 2
• D. 6

Answer: (B)

Verified step by step guidance

1. Understand the electron configuration of a neutral magnesium atom. Magnesium (Mg) has an atomic number of 12, meaning it has 12 electrons in its neutral state. The electron configuration is: 1s² 2s² 2p⁶ 3s².
2. Identify the electron configuration of the magnesium ion (Mg²⁺). When magnesium forms a Mg²⁺ ion, it loses two electrons. These electrons are removed from the outermost shell, which is the 3s orbital.
3. Determine the electron configuration of Mg²⁺ after losing two electrons. The configuration becomes: 1s² 2s² 2p⁶.
4. Recognize that the n = 3 shell corresponds to the third energy level, which includes the 3s and 3p orbitals. Since Mg²⁺ has lost its 3s electrons, there are no electrons left in the n = 3 shell.
5. Conclude that the number of electrons in the n = 3 shell of a Mg²⁺ ion is 0, as all electrons in this shell have been removed to form the ion.