Question

1. what is the process of solar nuclear fusion?

helium molecules are fused together and become hydrogen molecules, giving off large amounts of energy.
hydrogen atoms are fused into deuterium, then helium - 3, then helium - 4, each step giving off large amounts of energy.
hydrogen molecules are fused together and become oxygen molecules, giving off large amounts of energy.
hydrogen atoms are fused into deuterium, then helium - 4, then back into hydrogen, each step giving off large amounts of energy.

Explanation:

Solar nuclear fusion is a process in stars like the Sun. In the Sun, hydrogen atoms undergo a series of fusion reactions. First, hydrogen atoms fuse to form deuterium. Then, further fusion reactions occur where deuterium and other hydrogen - related nuclei combine to form helium - 3. Finally, helium - 3 nuclei fuse to form helium - 4. Each of these fusion steps releases a large amount of energy due to the mass - energy equivalence principle ($E = mc^{2}$), where a small amount of mass is converted into a large amount of energy.

• The first option is incorrect because the process in the Sun starts with hydrogen, not helium, and the direction of fusion is from lighter (hydrogen) to heavier (helium) nuclei, not the reverse.
• The third option is incorrect because hydrogen does not fuse directly to form oxygen in the Sun's core (oxygen formation is a more complex process that occurs in more massive stars in later stages of stellar evolution).
• The fourth option is incorrect because the process does not cycle back into hydrogen after forming helium - 4 in the main sequence phase of a star like the Sun.

Answer:

Hydrogen atoms are fused into deuterium, then helium - 3, then helium - 4, each step giving off large amounts of energy.