Final answer:
The reaction where glucose and galactose form lactose and water is best described as a synthesis reaction, specifically a biosynthetic reaction.
Step-by-step explanation:
The question pertains to the type of reaction that occurs when glucose and galactose combine to form lactose and water. The correct term that describes this process is B. Synthesis, specifically a biosynthetic reaction in which two monosaccharides, glucose and galactose, join to form the disaccharide lactose. This is achieved through a dehydration synthesis, which is the opposite of a hydrolysis reaction where water is used to break down compounds.