O Levels Chemistry (5070)•5070/12/M/J/21
Explanation
Gas identification by chemical properties
Steps:
- Property 1 (colourless) eliminates colored gases like chlorine.
- Property 2 (no litmus effect) rules out acidic or basic gases like chlorine and ammonia.
- Property 3 (no limewater effect) excludes CO2-containing or reacting gases, though none here match directly.
- Property 4 (flammable) matches hydrogen, which burns in air.
Why C is correct:
- Hydrogen (H₂) is colorless, neutral (no litmus reaction), inert to limewater, and highly flammable, forming water upon combustion (2H₂ + O₂ → 2H₂O).
Why the others are wrong:
- A. Ammonia: Basic, turns damp red litmus blue.
- B. Chlorine: Pale green-yellow color, acidic, bleaches litmus.
- D. Oxygen: Colorless and neutral but supports combustion, not flammable itself.
Final answer: C
Topic: Identification of ions and gases
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