NDA (I) 2025 General Ability Test · Question 76 of 150

Correct — A, CO. Carbon monoxide is a neutral oxide — neither acidic nor basic — and it does not form a salt with acids or bases under ordinary conditions. Carbon monoxide, along with water and nitrous oxide (N2O), makes up the classic set of neutral oxides.

• (b)CO2 — Carbon dioxide is an acidic oxide: it dissolves in water to give carbonic acid and reacts with bases, for example turning lime water milky.
• (c)Na2O — Sodium oxide is a basic oxide of a metal; it dissolves in water to give the strong base sodium hydroxide.
• (d)MgO — Magnesium oxide is a basic oxide; it reacts with acids to form salts and gives an alkaline solution in water.

Oxides are classified by their acid-base behaviour: non-metal oxides are usually acidic (CO2, SO2), metal oxides are usually basic (Na2O, MgO), some are amphoteric (Al2O3, ZnO), and a few non-metal oxides are neutral (CO, N2O, water).

The trap pairs CO with CO2 — the same two elements but opposite behaviour. Carbon dioxide is acidic; only carbon monoxide is neutral, while the two metal oxides are basic.

• Neutral oxides — CO, N2O and water — are neither acidic nor basic.
• CO2 and SO2 are acidic oxides that form acids with water.
• Na2O and MgO are basic oxides that form alkalis and react with acids.
• Al2O3 and ZnO are amphoteric — they react with both acids and bases.

• Confusing CO (neutral) with CO2 (acidic).
• Assuming every carbon oxide is acidic — CO is the neutral exception.

A straightforward 'which oxide is neutral, acidic, basic or amphoteric' classification item.

No directly related past PYQ was found.

• practice — not a real PYQ

  Which of the following is an amphoteric oxide?

  • (a)Na2O
  • (b)CO2
  • (c)Al2O3
  • (d)CaO

  Answer(c) Al2O3 — it reacts with both acids and bases.

• practice — not a real PYQ

  Which one of the following is an acidic oxide?

  • (a)MgO
  • (b)SO2
  • (c)Na2O
  • (d)CaO

  Answer(b) SO2 — a non-metal oxide that forms sulphurous acid in water.