Final answer:
Monosaccharides cannot be hydrolyzed into simpler sugars because they are the simplest carbohydrates, being either polyhydroxy aldehydes or ketones. Only larger sugar chains like disaccharides and polysaccharides can be hydrolyzed into monosaccharides.
Step-by-step explanation:
The statement that monosaccharides can be hydrolyzed to give polyhydroxy ketone but not aldehyde is incorrect. Monosaccharides are the simplest form of carbohydrates that cannot be hydrolyzed further into simpler sugars. They are either polyhydroxy aldehydes or polyhydroxy ketones, and their structures are such that they cannot be broken down by hydrolysis into smaller carbohydrate molecules. Monosaccharides like D-glucose and D-fructose are classified based on the presence of an aldehyde or ketone group and their carbon chain length, thus they are known as aldose or ketose sugars, respectively.
When larger carbohydrates such as disaccharides, oligosaccharides, and polysaccharides are hydrolyzed, they yield monosaccharides, not the other way around. Monosaccharides themselves are the building blocks for these larger sugar chains and can combine to form disaccharides and polysaccharides, which can indeed be broken down into monosaccharides through hydrolysis.