Answer:
If a small amount of br2 is added to an aqueous solution of an unknown monosaccharide, the reddish-brown color of br2 will disappear if the monosaccharide is an Aldose.
Step-by-step explanation:
This happens because the Aldose contains a carbonyl group called Alsedyde. Bromine being a oxidizing agent oxidizes the aldehyde functional group to Carboxylic Acid moiety. While this test is not positive in case of Ketonic Functional group.