Science — CBSE Class 10 board question

Zinc oxide is amphoteric because it shows the properties of both a basic oxide and an acidic oxide.

• It reacts with acids (behaving as a base):

ZnO + H₂SO₄ → ZnSO₄ + H₂O

• It reacts with bases (behaving as an acid):

ZnO + 2NaOH → Na₂ZnO₂ + H₂O

Since it neutralises both acids and bases, it is called an amphoteric oxide.

Source: Metals and Non-metals, Chapter 3

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• The examiner wants both reactions (with acid and with base) to award full marks. Simply stating "reacts with both acids and bases" without equations may cost marks in a 2–3 mark question.
• The key term to use is amphoteric — defined as an oxide that behaves as both acidic and basic.
• Aluminium oxide (Al₂O₃) is the other standard example of an amphoteric oxide from the same chapter.