Monosaccharides are simplest types of carbohydrate monomers formed of single aldehydic or ketonic derivative of polyhydroxy alcohols. On the basis of number of C -atoms they are of different types as:
(i) Trioses are those having 3 carbon atoms. e.g. glyceraldehyde, dihydroxyacetone.
(ii) Tetroses are those having 4 carbon atoms, e . g. erythrose, threose
(iii) Pentoses are those having 5 carbon atoms, e . g. ribose, xylulose, deoxyribose, arabinose, ribulose.
(iv) Hexoses are those having 6 carbon atoms, e.g. glucose, fructose, galactose, mannose.
(v) Heptoses are those having 7 carbon atoms, e.g. sedoheptulose, glucoheptose, galactoheptose