Final answer:
A magnesium atom loses two electrons to form a magnesium ion (Mg2+), which is a positively charged particle known as a cation with a charge of +2.
Step-by-step explanation:
When a magnesium atom loses two electrons, it forms a positively charged particle known as a cation. This is due to the fact that losing electrons yields a surplus of protons with respect to electrons, resulting in a positive charge.
Specifically, the name and symbol of the particle formed is a magnesium ion (Mg2+). The atom ends up with two fewer electrons than protons, giving it a charge of +2.