Question

Which of the following is a reducing sugar?

• A. Galactose
• B. Gluconic acid
• C. 3-Methyl galactoside
• D. Sucrose

Answer 1

The correct option is A Galactose

All those sugars which have a free aldehyde or a ketone group are called reducing sugars. These are able to reduce cupric ions $\left(C{u}^{+2}\right)$ into cuprous ions $\left(C{u}^{+}\right)$. The two common tests are Benedict's test and Fehling's test. Both tests employ alkaline solution of copper sulphate which is blue in colour, with reducing sugar it gives orange to brick red precipitation.

Galactose is a reducing sugar. It gives a brownish red precipitate with Fehling's reagent and with Benedict's reagent, it gives yellow or green precipitate confirming the presence of sugar. Sucrose, starch are non-reducing sugars.