In the Osazone formation, only the first two atoms, C1 and C2 take part thus other reducing sugars that differ in configuration at C1 and C2 and have the rest of the structure with the same (e.g. C3, C4, C5) configuration. It gives the same osazones during Osazone formation and the structural dissimilarity at C1 and C2 disappears. Glucose, mannose and fructose cannot be distinguished by osazone test because they give the same osazones.