Which statement best describes the process of nuclear fusion?

a. Smaller nuclei combine to make a larger nucleus.

b. A large nucleus is broken down into free protons and neutrons.

c. Hydrogen atoms bond together to make molecular hydrogen.

d. Hydrogen and helium gas are burned to produce heat and electricity.

a. Smaller nuclei combine to make a larger nucleus.

Explanation:

Nuclear fusion is the process by which several atomic nuclei of similar charge bind and form a heavier nucleus.

In order for fusion to occur, an important energy barrier produced by electrostatic force must be overcome. Over long distances, two nuclei repel each other due to the electrostatic repulsion force between their protons, positively charged. However, if two nuclei can be approached sufficiently, due to the strong nuclear interaction, which is greater over short distances, electrostatic repulsion can be overcome, and fusion takes place.