If a substance loses electrons, does it become oxidized or reduced?

When a substance loses electrons, it undergoes oxidation. This process is characterized by the loss of negatively charged particles (electrons), leading to an increase in the oxidation state of that substance. Oxidation is one half of the redox (reduction-oxidation) reaction, where one species loses electrons (is oxidized) and another gains electrons (is reduced).

For instance, consider a simple redox reaction involving magnesium and oxygen. When magnesium (Mg) reacts with oxygen (O2), magnesium loses two electrons, transforming into Mg²⁺ ions. This loss of electrons signifies that magnesium has been oxidized. Oxygen, conversely, gains electrons to form oxide ions (O²⁻), indicating that it has been reduced.

Thus, the correct response is that a substance that loses electrons is classified as oxidized, which aligns with the fundamental principles governing redox reactions in biochemical and chemical contexts.