Number of optical isomers possible for Glucose is
2
4
8
16
Leber van Hoft rule for the number of stereoisomers is 2n where 'n' is the number of chiral centers. In open chain of glucose, there are 4 chiral centers. Hence it is 24 =16 isomers.Glucose, with four asymmetric carbon atoms, can form 16 isomers.Sugars have large numbers of stereoisomers because they contain several asymmetric carbon atoms.Ref: Harper&;s Biochemistry; 30th edition; Chapter 15; Carbohydrates of Physiological Significance
Structure and function of protein