I think you forgot to give the options along with the question. I am answering the question based on my knowledge and research. "Test a third group that does not receive the supplement" would be the procedure that would have made the <span>outcome of this study more valid. I hope the answer helps you.</span>
Answer:
Heat, light and electricity can all be used to move electrons between orbitals. The electrons are what allow atoms to react with each other in chemical reactions, and they are also what cause certain compounds to emit light when heated. When an atom is heated up, it starts to vibrate intensely. I hope this helped you. :)