Why are the products of nuclear fusion slightly less massive than the reactants

Because during nuclear fusion the mass of products escapes in the form of energy. This happens in any chemical reaction, but in nuclear reactions the mass that escapes is much greater.

Explanation:

Nuclear fusion is called the process of combining two atomic nuclei to form a third heavier element. When the new element is formed, energy is released. This released energy is a large part of the reactants' mass. As a result, products are slightly less massive than reagents.

Nuclear mergers do not occur naturally here on Earth. To shock two equal elements and create a fusion, an enormous amount of energy is needed to overcome the electrostatic repulsion force between the elements. This repulsion force is called the Coulomb barrier.

the answer is trees if i'm not mistaken

not sure if this is what you'r looking for eubacteria and archaebacteria