What is the test for chlorine gas?

The test for chlorine gas involves using damp red litmus paper, which is known to turn white when exposed to chlorine. This occurs because chlorine is a bleaching agent; it reacts with the dye in the litmus paper, effectively decolorizing it. This property makes it a specific and effective method to identify the presence of chlorine gas in a sample.

The other choices do not accurately reflect the properties of chlorine or how it can be detected. For instance, turning red litmus paper blue indicates the presence of a basic substance, which is not relevant to chlorine. A burning splint that burns quickly is indicative of a flammable gas, not chlorine. Using a pH indicator that turns green suggests neutrality and does not provide specific information about chlorine's presence. Thus, the method involving bleached litmus paper is the most appropriate for confirming chlorine gas.