Which of the following substances is an example of a polyhydroxy alcohol?

Sorbitol is an example of a polyhydroxy alcohol because it contains multiple hydroxyl (-OH) groups in its molecular structure. Polyhydroxy alcohols, also known as sugar alcohols, typically have at least two hydroxyl groups, which contribute to their classification. Sorbitol specifically has six carbon atoms, along with six hydroxyl groups, making it a suitable representative of this category.

Glycerol, while it also qualifies as a polyhydroxy alcohol due to its three hydroxyl groups, is not the answer because the focus in this context is on the most common sugar alcohol in the options given. Fructose is classified as a sugar, specifically a ketose, and does not fit the definition of a polyhydroxy alcohol in the context of the question. Glucose, like fructose, is a simple sugar (an aldose) and also does not fulfill the criteria; it has multiple hydroxyl groups but does not fall into the same category as sugar alcohols. Thus, within the provided choices, sorbitol stands out as the prime illustration of a polyhydroxy alcohol.