Mass is lost or gains in

a.) all chemical reactions
b.) all nuclear fission reactions
c.) all nuclear fusion reactions
d.) all chemical and nuclear reactions

my guess is B

To determine which option is correct, let's analyze each type of reaction:

a) Chemical reactions: In chemical reactions, atoms rearrange to form new substances. The law of conservation of mass states that mass is neither created nor destroyed during a chemical reaction. Therefore, the mass of the products should be equal to the mass of the reactants. This means that there is no net loss or gain of mass in chemical reactions. So, option a) is incorrect.

b) Nuclear fission reactions: In nuclear fission, heavy atomic nuclei split into smaller nuclei, releasing energy. Although a small amount of mass is indeed converted into energy according to Einstein's famous equation E=mc², the mass loss is usually insignificant as the total energy released is enormous compared to the mass. However, it is important to note that in nuclear fission reactions, some mass is converted to energy, resulting in a net loss of mass. Therefore, option b) is incorrect.

c) Nuclear fusion reactions: In nuclear fusion, light atomic nuclei combine to form a heavier nucleus, also releasing energy. Like in nuclear fission, a small amount of mass is converted into energy. However, due to the high energy requirements for fusion and the subsequent release of much larger amounts of energy, the mass loss is also typically negligible. Therefore, option c) is incorrect.

d) All chemical and nuclear reactions: Considering the explanations given above, the only correct option remains d) all chemical and nuclear reactions. Chemical reactions do not result in a net loss or gain of mass, while both nuclear fission and fusion reactions involve the conversion of a small amount of mass into energy, resulting in a net loss of mass during the reactions.

In conclusion, the correct answer is d) all chemical and nuclear reactions.