Oxidation is best described by which statement?

• A. Increase in oxidation number
• B. Gain of electrons
• C. Decrease in oxidation number
• D. Occurs only in presence of water

Answer: (A)

Oxidation is defined by an increase in oxidation state (oxidation number) of the element involved. When a species is oxidized, its oxidation number goes up because it has effectively lost electrons, making it more positively charged overall. In redox chemistry, oxidation and reduction are paired: oxidation increases the oxidation state, while reduction decreases it. Gaining electrons is the opposite process—reduction. The idea that oxidation only happens in water is incorrect; oxidation can occur in many environments, including dry or non-aqueous settings.