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What is oxidation?

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Quick answer

Oxidation is a chemical reaction in which a substance loses electrons — often by combining with oxygen. Rusting iron, a browning apple, and burning fuel are all oxidation, and it is always paired with 'reduction,' where another substance gains those electrons.

Key things to understand

  1. At its core, oxidation is the loss of electrons by an atom or molecule.
  2. It often involves oxygen, as in rust, fire, and respiration.
  3. It always pairs with reduction (electron gain) — together called redox.
  4. It releases energy in burning and in your cells' use of food.
  5. Antioxidants are substances that slow unwanted oxidation.

People also ask

Is oxidation always about oxygen?
Not strictly — the modern definition is loss of electrons, but it's named after oxygen because oxygen so commonly causes it.
What is a redox reaction?
A paired reaction where one substance is oxidized (loses electrons) while another is reduced (gains them).
What do antioxidants do?
They donate electrons to neutralize reactive molecules, slowing harmful oxidation in food and in the body.