Student has accidentally mixed up a bottle of ethanoic acid, hexane and hex-2-ene, how does pupil tells difference between the three bottles?

pH paper or smelling will identify the ethanoic acid. Then, you can distinguish the hexane from hex-2-ene by shaking the liquid with a small amount of bromine water. The alkene will decolorize the bromine water, but the alkane will not.

Ethanoic acid: (acetic acid:) A drop dissolves in water. Does not decolorize bromine.
Hexane: A drop does not dissolve in water. Does not decolorize bromine.
Hexene: A drop does not dissolve in water. Decolorizes bromine (usually done in CCl4)

Test each one.