Final answer:
Lactose is a disaccharide made of glucose and galactose with one water molecule removed during formation, leading to the molecular formula C12H22O11 (Option B).
Step-by-step explanation:
The student is asking about the molecular formula for lactose, which is a disaccharide composed of one glucose monomer and one galactose monomer. Since both glucose and galactose have the molecular formula C6H12O6, and considering that during the formation of lactose one molecule of water (H2O) is removed in the dehydration synthesis reaction, the correct molecular formula for lactose would be C12H22O11. Therefore, the correct answer is B) C12H22O11.