Glucose — found in plants and animals (It is the energy source for cellular respiration)
Fructose — found in fruits and honey
Galactose — present in milk
They are reducing sugars, they can remove oxygen from other compounds..
They can be detected by using Fehling's or Benedict's test.
When monosaccharides are heated with Fehling's or Benedict's solution, they will reduce the blue copper(II) sulphate in the two solutions to a brick red precipitate.