Biomolecules Part 1

A non-reducing sugar is one kind of carbohydrate that is not oxidised by a weak oxidising agent (an oxidising agent that oxidises aldehydes but not alcohols, such as the Tollen's reagent) in a basic aqueous solution.

While all others, i.e. glucose, fructose and galactose are reducing sugarThus, sugar (A) is sucrose.