Which of the following oxides is amphoteric?

Step 1: Analyze the question We need the oxide that is amphoteric, meaning it reacts with both acids and bases to form salts and water.

Step 2: The concept

• Acidic oxides (non-metal oxides such as CO₂, SO₂, NO₂) react with bases.
• Basic oxides (metal oxides such as CaO, Na₂O, MgO) react with acids.
• Neutral oxides (CO, H₂O, N₂O) react with neither.
• Amphoteric oxides react with both acids and bases. The common ones are ZnO, Al₂O₃, PbO, SnO (remember "Zebra And Pig Stay"... or simply Zn, Al, Pb, Sn).

Step 3: Check each option

• A. Carbon(II) oxide (CO): Neutral oxide. It does not react with acids or bases under normal conditions.
• B. Nitrogen(IV) oxide (NO₂): Acidic oxide. It dissolves in water to give HNO₃ and HNO₂, and it reacts with bases.
• C. Lead(II) oxide (PbO): Amphoteric. • With acid: PbO + 2HNO₃ → Pb(NO₃)₂ + H₂O • With base: PbO + 2NaOH + H₂O → Na₂[Pb(OH)₄] (sodium plumbite)
• D. Calcium oxide (CaO): Basic oxide. It reacts with acids only: CaO + 2HCl → CaCl₂ + H₂O.

Step 4: Answer Lead(II) oxide is the amphoteric oxide, which is option C.

Tip: Metals that give amphoteric oxides sit near the "staircase" between metals and non-metals in the periodic table or are post-transition metals. Memorize Zn, Al, Pb, Sn. Group 1 and 2 metal oxides (like CaO) are basic, and non-metal oxides are acidic or neutral.