Final answer:
The correct Lewis symbol for a neutral atom of magnesium is A) Mg: , representing two valence electrons around the element symbol.
Step-by-step explanation:
The correct Lewis symbol for a neutral atom of Mg (magnesium) is A) Mg:. This is because a neutral magnesium atom has two valence electrons. These two electrons are represented as two dots next to the element symbol of Mg.
The alkaline earth metal magnesium has the atomic number 12, meaning it has 12 protons. In its neutral state, it also has 12 electrons. The valence shell of magnesium, which determines its Lewis symbol, is the third shell (3s), containing two electrons.
To achieve a noble gas configuration, magnesium tends to lose two electrons to form a Mg2+ ion. However, the question asks for the Lewis symbol of the atom, not the ion. Therefore, we depict the two valence electrons as dots around the Mg symbol for the neutral atom.