Final answer:
When glucose forms a ring, a six-membered cyclic structure known as a pyranose is created, involving the former carbonyl group and the fifth carbon's hydroxyl group, without loss of an oxygen atom.
Step-by-step explanation:
When glucose forms a ring, it undergoes a structural transformation where the linear form of the molecule changes to form a cyclic structure. In this process, the aldehydic group on the first carbon of glucose reacts with the hydroxyl group on the fifth carbon, resulting in the formation of a hemiacetal, creating a six-membered ring structure known as a pyranose. Consequently, the correct answer to the question is (e) Both (a) and (c). The molecule does not lose its carbonyl group but rather it becomes part of the new cyclic hemiacetal structure, and it definitely does not lose an oxygen atom. Lastly, the sixth carbon is not involved in forming the bond with the first carbon atom; instead, the oxygen atom also becomes a part of the ring.