Identifying gas by chemical properties and reactivity

Steps:

• Property 1 (colourless) eliminates chlorine, which is pale green.
• Property 2 (no litmus effect) eliminates ammonia (basic, turns red litmus blue) and chlorine (acidic, bleaches litmus), leaving hydrogen and oxygen.
• Property 3 (no limewater effect) fits both hydrogen and oxygen, as neither produces CO2.
• Property 4 (flammable) selects hydrogen, which ignites and burns in air, unlike oxygen.

Why C is correct:

• Hydrogen (H₂) is a diatomic, colorless, neutral gas that combusts with oxygen per 2H₂ + O₂ → 2H₂O.

Why the others are wrong:

• A. Ammonia: Basic gas (NH₃) that turns damp red litmus blue.
• B. Chlorine: Pale green gas that bleaches litmus paper.
• D. Oxygen: Supports combustion but is not itself flammable.

Final answer: C