Final answer:
Statement 2, which asserts that the sum of mass and energy is conserved, is true for both chemical and nuclear reactions; whereas Statement 1 applies only to chemical reactions.
Step-by-step explanation:
When considering whether mass is conserved during a reaction, we need to differentiate between chemical reactions and nuclear reactions.
For chemical reactions, the law of conservation of mass holds true; this states that the mass of the reactants is equal to the mass of the products. Energy changes in these reactions are usually insignificant in terms of mass. Therefore, Statement 1 is valid for chemical reactions.
However, when it comes to nuclear reactions, the law of conservation of mass and energy applies. This is because the energy changes involved are so large that they correspond to changes in mass (Einstein's equation E=mc² explains how mass and energy are interchangeable). So, in nuclear reactions, mass alone is not conserved; instead, the total sum of mass and energy remains constant. This means that Statement 2 is valid for nuclear reactions.
In conclusion, for both nuclear and chemical reactions, statement 2 is the accurate statement, which states that the sum of mass and energy is conserved during the reaction. Hence, b. Only 2 is the correct option.