What is the test for carbon dioxide gas?

The correct answer highlights a well-established method for identifying carbon dioxide gas, which involves reacting the gas with limewater. When carbon dioxide is bubbled through limewater, it reacts with calcium hydroxide (present in limewater) to form calcium carbonate. This reaction causes the limewater to turn from clear to milky, indicating the presence of carbon dioxide.

This phenomenon occurs because calcium carbonate is insoluble in water and forms a precipitate, which gives the solution a cloudy appearance. This method is widely used in laboratories due to its simplicity and reliability. Understanding this reaction is crucial for recognizing how carbon dioxide behaves in chemical contexts and its interactions with other substances, particularly in tests for gases.

The other options do not accurately reflect how carbon dioxide is tested. For instance, inserting a glowing splint into a test tube would only indicate the presence of oxygen and not carbon dioxide. Similarly, turning limewater clear would not occur with carbon dioxide. Lastly, using pH paper may show acidification but is not a direct test for carbon dioxide specific to its interaction with limewater.