A test tube contains a pure colourless gas. It is either oxygen, carbon dioxide, hydrogen or nitrogen. When a burning splint is put into the gas it just goes out. you are allowed only one more test to identify the gas. Say what the test is, and how you would reach your answer.

The next test would be the lime water test.

Explanation:

If placing the gas in lime water will turn the solution milky, then the gas is most probably carbon dioxide, the lime water (Ca(OH)₂) turns milky due to the formation of solid CaCO₃ that is insoluble after reaction with carbon dioxide.

Carbon dioxide also puts out the flame in the splint test because it does not support combustion.