Oxidation involves which of the following?

• A. Loss of electrons
• B. Gain of electrons
• C. Loss of oxygen
• D. Gain of hydrogen

Answer: (A)

Oxidation is about electron transfer. When a substance loses electrons, its oxidation state increases, making it the oxidized partner in a redox pair. This is the fundamental idea: oxidation corresponds to loss of electrons, while the species that gains electrons is reduced. For example, iron can lose electrons to oxygen in rust formation, so iron is oxidized and oxygen is reduced.

The other descriptions don’t fit as universally. Gaining electrons is reduction, not oxidation. The phrases about losing oxygen or gaining hydrogen come from older ways of thinking and don’t define oxidation in all reactions, since you can have oxidation without any change in oxygen or hydrogen atoms, as long as electrons are lost.