Since there are no choices provided for this question, the answer to why many scientists reject the cold fusion theory is that the experiment by Fleischmann and Pons that had the strongest claim was found out to be flawed. Many scientists who also replicated the experiment failed to obtain positive results which further weakened the claim for cold fusion theory.
The answer is A, a new chemical substance has to be formed for there to be a chemical change. This is because chemical change happens when a phase of matter changes due to chemicals.
