ANSWER

Pure glucose serves as a reference point, and is given a Glycemic Index (GI) of 100. Sucrose which is comprised of glucose and fructose, has a GI of 65. Galactose on the other hand has a lower GI compared with Fructose (GI=23) as it elicits a lower glycaemic response than fructose.

Reference

Wolever, T. M. S. (2006). The Glycaemic Index: A Physiological Classification of Dietary Carbohydrate (pp. 64-69). Oxfordshire: CABI Publishing.