Glucose is a hexose monosaccharide. It is one of the three major monosaccharides along with fructose and galactose. These are carbohydrates with a general formula of Cₓ(H₂O)ₓ, where x could be any number.
Now, you don't have to know the structural formula of the glucose to answer this. Just account all the elements in the glucose. You know that there are 6 oxygen atoms all in all. One of them belongs to the single carbonyl group. Consequently, that would mean that the remaining 5 oxygen atoms bond with hydrogen atoms to form 5 OH groups.
Just to be sure let us refer to the structural formula of glucose shown in the picture. It indeed has 5 OH groups.
Now, you don't have to know the structural formula of the glucose to answer this. Just account all the elements in the glucose. You know that there are 6 oxygen atoms all in all. One of them belongs to the single carbonyl group. Consequently, that would mean that the remaining 5 oxygen atoms bond with hydrogen atoms to form 5 OH groups.
Just to be sure let us refer to the structural formula of glucose shown in the picture. It indeed has 5 OH groups.