Final answer:
The correct answer is Oxidation. Phase I reactions in biotransformation involve various processes, such as oxidation, reduction, and hydrolysis.
Step-by-step explanation:
Phase I reactions in biotransformation involve various processes, such as oxidation, reduction, and hydrolysis, which help in breaking down foreign or physiological substances in the body. Oxidation reactions involve the addition of oxygen or the removal of hydrogen from a molecule. For example, alcohols can be oxidized to corresponding acids.