What is D-Glucose?
D-glucose is themolecule we have been discussingin class, and is the abundant form of th esugar. L-glucose is a stereoisomer of D-glucose, having the opposite orientation of the hydroxyl groups on all 4 asymmetric carbons of the sugar (2,3,4, and 5). carbon atoms 2-6?
Yes, it matters greatly. If there is a different arrangement of the hydroxyls around carbons 2-5 (left or right), then the hydroxyls will be differently oriented in 3-D space in the ring form; and indeed, the sugar will even have a different name. Switch one hydroxyl from left to right (or right to left) and you get mannose, or galactose, etc.). These different sugars are stereoisomers of each other, as in L and D amino acids. Because hexoses have 4 asymmetric carbons, there can be 2^4 = 16 different arrangements, 16 different stereoisomers, each with its own name and its own distinctive 3-dimensional configuration. See text and problems.

In question 1.23(b) in the problem book it asks for the orientation of the #4 carbon of galactose in the chair form, yet the answer key states that all -OH groups are equatorial for glucose. Is the question supposed to state glucose or galactose?
Admittedly, the answer is a bit terse and even misleading, stating simply that in glucose all the OHs ore equatorial. Moreover, it is not even correct, as in alpha-glucose the the C1 OH is axial and down. Thanks for catching this. A better answer is:

In glucose, the hydroxyls at C2, C3 and C4 are aways equatorial and out. (This fact need not not be meorized, as you are told to view a diagram of glucose in the chair conformation.) In galactose, it is stated that the orientation of the H and OH at C4 are opposite that of glucose. Thus in galactose, the the OH must be axial rather than equatorial, and so the H must be equatorial.