Which of the following is a common reducing agent used in labeling processes?

Ascorbic acid is commonly used as a reducing agent in labeling processes, particularly in nuclear medicine. Its chemical properties allow it to effectively donate electrons, which is essential for the reduction of metal ions and other compounds during the labeling process. This ability to reduce substances is crucial in the preparation of radiopharmaceuticals, as it helps in the stabilization of radiolabeled compounds and enhances the efficiency of the labeling reaction.

In the context of nuclear medicine, when radiopharmaceuticals are created, reducing agents like ascorbic acid can prevent oxidation of the active components, thus maintaining the integrity and efficacy of the final product. Additionally, ascorbic acid is relatively safe and can be used in a variety of formulations without significant side effects, making it a preferred choice among the reducing agents used for labeling processes in nuclear medicine.