To identify a non-reducing sugar from the options provided, we need to consider the structure and chemical reactivity of each. Reducing sugars are those that have a free aldehyde or ketone group capable of acting as a reducing agent, typically through an oxidation-reaction where the sugar is oxidized while reducing another compound. Non-reducing sugars, on the other hand, do not have such free reactive groups. Below, l'll explain the structure of each sugar given in the options to identify the non-reducing sugar. Sucrose: Sucrose is a disaccharide composed of glucose and fructose units. It is unique because in its structure, the anomeric carbon of glucose (which is the carbon linked to both the oxygen in the ring and the −CH‌2‌OH group outside the ring) is involved in the glycosidic bond with the anomeric carbon of fructose. As a result, neither glucose nor fructose parts of sucrose have a free anomeric carbon capable of acting as a reducing agent. Since the defining groups that classify sugars as reducing are "locked away" in the glycosidic bond, sucrose is considered a non-reducing sugar. Maltose: Maltose is a disaccharide made up of two glucose units. In the structure of maltose, one of the glucose units has a free anomeric carbon that is not involved in the glycosidic bond. This free anomeric carbon allows maltose to act as a reducing sugar. Lactose: Lactose is a disaccharide composed of glucose and galactose units. Similar to maltose, lactose has a free anomeric carbon on the galactose part of the molecule, which is not involved in the glycosidic bond, thus permitting lactose to behave as a reducing sugar. Glucose: Glucose is a monosaccharide with an aldehyde group, allowing it to be oxidized and hence act as a reducing sugar. Therefore, glucose is indeed a reducing sugar. Given this information, the correct answer is: Option A - Sucrose, as it is the only non-reducing sugar in the list due to both anomeric carbons being involved in the glycosidic bond. Therefore, it cannot participate in redox reactions that are characteristic of reducing sugars.