What are monosaccharides?

(N/A) Monosaccharides are the simplest form of carbohydrates that cannot be hydrolysed further into smaller polyhydroxy aldehyde or ketone units.
They are classified based on the number of carbon atoms and the functional group present.
$1$. If they contain an aldehyde group,they are called aldoses.
$2$. If they contain a keto group,they are called ketoses.
Additionally,they are classified as trioses,tetroses,pentoses,hexoses,or heptoses based on the number of carbon atoms ($3, 4, 5, 6, 7$ respectively). For example,a ketose with $3$ carbon atoms is a ketotriose,and an aldose with $3$ carbon atoms is an aldotriose.