Final answer:
The ribose sugar differs from deoxyribose sugar in DNA by having a hydroxyl group at the 2' carbon, which deoxyribose lacks.
Step-by-step explanation:
The part of the ribose sugar that is different from the deoxyribose sugar used in DNA is pointed to by arrow 2'. This is because ribose has a hydroxyl group at the 2' carbon, while deoxyribose lacks this hydroxyl group, having only a hydrogen atom attached to its 2' carbon. This absence of the hydroxyl group at the 2' position is what gives deoxyribose its name, as it is "de-oxy" indicating "without oxygen" at that particular carbon.