Describe what will be seen when compound A is shaken with bromine water.

The test for an alkene (a compound containing a C=C double bond) is to shake it with bromine water. Bromine water is an aqueous solution of bromine, which has a distinct orange-brown or yellow colour. Alkenes undergo an addition reaction with bromine, where the double bond breaks and a bromine atom adds to each of the two carbon atoms. The product, a dibromoalkane, is colourless. Because the bromine is used up in the reaction, its colour disappears. Therefore, a positive test for an alkene is that the orange/brown/yellow bromine water is decolourised (turns colourless).