Which of the following gases turns limewater milky?

Correct option is D

The correct answer is (d) Carbon dioxide.
· Carbon dioxide (CO₂) turns limewater (a solution of calcium hydroxide) milky because it reacts with calcium hydroxide to form calcium carbonate, which is insoluble and gives the solution a milky appearance.
The reaction is: Ca(OH)2+CO2→CaCO3+H2O
Information Booster:
· Oxygen and hydrogen gases do not cause limewater to turn milky.
· This reaction is commonly used as a test for the presence of carbon dioxide.
Additional Information:
· If excess carbon dioxide is passed through limewater, the milky solution may clear again due to the formation of calcium bicarbonate, which is soluble in water.