Final answer:
The molecular formula for a middle glucose molecule in starch is C6H12O6, as each glucose unit retains this formula even after linking to form starch.
Step-by-step explanation:
The molecular formula for glucose is C6H12O6. This is because a single molecule of glucose contains 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. When glucose molecules join to form starch through a condensation reaction, a molecule of water (H2O) is removed for each bond formed between glucose units. However, when considering just a middle glucose molecule in a starch chain, this water removal has already occurred at its links to adjacent glucose molecules, so the formula remains C6H12O6. The correct answer to the molecular formula of starch based on the middle glucose molecule is therefore option B.