He is a polymer made of n C6H12O6 dehydrated polymer by hydroxyl and aldehyde group to remove a molecule of water, but that a molecule of water exactly how to remove is not necessarily, so starch is not necessarily pure, it is a mixture of many molecular formula for the same (C6H12O6)n material It is a mixture of many substances with the same molecular formula (C6H12O6n), so at the middle school level only the definite functional group is discussed

That is hydroxy-OH