Which of the following reagents is used to distinguish between ethene and ethane?
Correct: B
Ethene is an unsaturated hydrocarbon (alkene) and will decolorize reddish-brown bromine water due to an addition reaction. Ethane is a saturated hydrocarbon (alkane) and will not react with bromine water under normal conditions, so it will not decolorize it. This is a common test for unsaturation.