Which of the following causes macromolecules to be classified as organic molecules? carbon hydrogen nitrogen oxygen

Carbon is the answer you are looking for. However, not all carbon containing molecules are organic. Examples being carbon oxides such as CO (carbon monoxide) and CO2 (carbon dioxide). Some Chemists classify organic compounds as having a C-H bond present but this is not completely correct as this excludes molecules like benzenehexol (benzene with an alcohol group on each carbon rather than a hydrogen) which are considered organic. A solid definition of an organic molecule is not certainly agreed. Just remember that: all organic molecules contain carbon but not all carbon containing molecules are organic.