Final answer:
The fusion of light nuclei into heavier ones occurs in the Sun's core, where the conditions are right for nuclear fusion. This process releases energy that we see as sunlight. The correct answer is option a.
Step-by-step explanation:
The fusion of light nuclei to produce heavier ones occurs in the core of the Sun. The Sun's core is where the temperature and pressure are high enough to facilitate nuclear fusion reactions. During this process, lighter nuclei such as hydrogen are combined to form heavier elements like helium, releasing a tremendous amount of energy. This energy is eventually radiated out from the Sun, reaching the photosphere and escaping into space as sunlight.
Nuclear fusion is a process that powers the stars, including our Sun, and it is fundamentally different from fission, which involves splitting heavier nuclei into lighter ones. The fusion process continues in a sequence of stages with heavier elements being produced in the cores of massive stars under even more extreme conditions, eventually leading to the creation of elements like iron.