Which observation shows oxygen supports combustion?

• A. The glowing wooden splint relights in the gas
• B. A blue litmus paper turns red
• C. A red litmus paper turns blue
• D. No change occurs when a glowing splint is inserted

Answer: (A)

Oxygen is an oxidizer that supports combustion, so a burning or glowing material can keep burning or rekindle when placed in an oxygen-containing gas. Seeing a glowing wooden splint relight in the gas shows that oxygen is present and can sustain the flame.

The other observations aren’t about burning. Litmus tests indicate acidity or basicity, not whether a gas can support combustion. No change with the glowing splint means the gas doesn’t provide the needed oxygen, so it can’t support burning.