ketone (fructose) group allows them to change between their open and cyclic forms easily. This helps the sugars’ reducing ability which explains why they were the first to change color (best reducers). Lactose was the last to change color (excluding sucrose that did not change) because it is a disaccharide containing two sugar molecules (galactose and glucose). Lactose must first open its ring in order to expose it’s carbonyl group before oxidation can occur. This explains why it was the last to change color