Answer:
The correct answer is- Oxygen
Step-by-step explanation:
In cellular respiration one glucose molecule is oxidized into 6 molecules of carbon dioxide and 6 molecule of water . This oxidation of glucose release energy which is used to make ATP. ATP is the form of energy which can be be used by the cell to perform its metabolic function.
The reactants that are necessary for cellular respiration are C₆H₁₂O₆ and O₂ and the product of cellular respiration is CO₂, H₂O, and ATP. Some of the energy released during the oxidation of glucose in cellular respiration is released as heat in the surrounding.
Therefore the oxygen is the necessary reactant for cellular respiration to occur.