Which gas would cause both limewater to turn milky and a glowing splint to be extinguished?

• A. Hydrogen
• B. Oxygen
• C. Carbon dioxide
• D. Nitrogen

Answer: (C)

This question is about how a gas interacts with limewater and with a glowing splint to identify it. Limewater is calcium hydroxide solution, and when carbon dioxide dissolves in it, a chemical reaction forms calcium carbonate, which is insoluble and appears as a cloudy, milky mixture. That milky appearance is a classic sign of carbon dioxide.

A glowing splint tests for the presence of oxygen because flames and glowing embers rely on oxygen to keep burning. In a gas that does not support combustion, the splint will go out. Carbon dioxide does not support combustion, so a glowing splint will be extinguished in it.

So carbon dioxide is the gas that both makes limewater turn milky and extinguishes a glowing splint.