Test for oxygen gas which observation is expected?

• A. Squeaky pop with a lit splint
• B. Relights a glowing splint
• C. Turns limewater cloudy
• D. Damp red litmus turns blue

Answer: (B)

Oxygen supports combustion, so a glowing splint will relight when exposed to a gas that contains oxygen. The glow of the ember flares back into a flame because the extra oxygen around it makes burning more vigorous. That’s why the expected observation is that the glowing splint relights.

Consider what the other tests detect: a squeaky pop comes from hydrogen reacting with oxygen to form water, limewater turning cloudy indicates carbon dioxide, and damp red litmus turning blue shows a basic gas like ammonia. None of those indicate the presence of oxygen, which is why they don’t match this test.