Which result indicates carbon dioxide extinguishes a lit splint?

• A. Carbon dioxide extinguishes a lit splint.
• B. Hydrogen extinguishes a lit splint.
• C. Air makes a flame flare.
• D. Oxygen accelerates combustion.

Answer: (A)

The key idea is that a flame needs heat, fuel, and oxygen to keep burning. Carbon dioxide cannot supply oxygen, and it’s heavier than air, so it blankets the flame and slows away the oxygen around it. With less oxygen available and the heat being spread into the surrounding gas, the splint’s flame cannot sustain itself and goes out. That’s why seeing a lit splint go out in carbon dioxide demonstrates that this gas does not support combustion.

In contrast, hydrogen is a fuel that can burn, air can supply more oxygen so flames can flare, and oxygen itself speeds up burning, so those observations don’t show extinguishing by a non-supporter like carbon dioxide.