How do yout explain the presence of five `-OH` groups in glucose molecule?

Explanation

Glucose gives pentaacetate derivative on acetylation with acetic anhydride.
`{:(" "CHO),(" |"),(" "(CHOH)_(4)),(" |"),(" "CH_(2)OH):}+underset("anhydride")underset("Acetic")underset()(5(CH_(3)CO)_(2)O)overset(ZnCl_(2))underset("Heat")rarrunderset("Glucose pentaacetate")({:(" "CHO),(" |"),((CHOCOCH_(3))_(4)),(" |"),(CH_(2)OCOCH_(3)):})+5CH_(3)COOH`
This confirms the presence of five `-OH` groups.