Question

Which one of these will not give red precipitate with benedict's solution?

Answer 1

Only alliphatic aldehyde gives benedict test possitive aromatic aldehyde does not give this reaction

Answer 2

Answer:  

A reducing sugar can give away electrons thereby getting oxidized by itself and reducing a certain reagent, while non-reducing sugar lacks this ability. They also do not have free ketone or aldehyde group. When Benedict’s solution is heated with a reducing sugar, an insoluble compound is found which in red in colour.

This precipitate is copper oxide. And the colour change is caused by the reducing property of reducing sugar like glucose, fructose and maltose. The colour change is due to reduction of Cu (II) ions present in the Benedict’s solution to Cu(I)ions.