Concept:Benedict's solution is used to test for reducing sugars like glucose, which give a brick-red colour when warmed.
Explanation:Benedict's solution is a blue reagent that contains copper(II) ions (
Cu2+).
Glucose is a reducing sugar, so when it is warmed with Benedict's solution, glucose reduces the copper(II) ions to copper(I) ions.
An insoluble brick-red precipitate of copper(I) oxide (
Cu2O) is then formed.
Starch and egg white are not reducing sugars, so they do not produce this colour change with Benedict's solution.
The appearance of the brick-red precipitate is therefore a positive confirmation of glucose.
Answer:A. Glucose