Question

How many electrons are in the n = 3 shell of a magnesium ion (Mg)^(2+)?

A) 2
B) 6
C) 8
D) 12

Answer 1

A magnesium ion (Mg)^(2+) has no electrons in the n = 3 shell because it loses its two 3s electrons upon ionization, leaving the n = 3 shell empty.

Step-by-step explanation:

The student asked how many electrons are in the n = 3 shell of a magnesium ion (Mg)^(2+). A neutral magnesium atom has an atomic number of 12, which means it has 12 protons and, when neutral, has 12 electrons. The electron configuration of neutral magnesium is [Ne]3s², indicating that it has two electrons in the 3s subshell, which is the first part of the n = 3 shell. However, when magnesium loses two electrons to become Mg^(2+), it loses the two 3s electrons, leaving the n = 3 shell empty. Therefore, the correct answer to the question is A) 0 electrons, which was not provided as an option.