I think the answer is H in glucose and water and O in O2. Photosynthesis is the process in which green plants and other organism convert light energy to chemical energy which is used in activities within the organism. Water that is exposed to the plant reacts with carbon dioxide to produce sugar and oxygen. The radioactive O will hence show up in the oxygen molecule and the radioactive H shows up in the sugar/ glucose molecule.
When no ions are produced, or the ion content is low, the solute is a non-electrolyte. Non-electrolytes do not conduct electricity or conduct it to a very small degree. In an aqueous solution a strong electrolyte is considered to be completely ionized, or dissociated, in water, meaning it is soluble
