The source of the energy emitted by the Sun is the result of reactions involving hydrogen nuclei in the Sun's core.

The energy emitted by the Sun comes from a process called nuclear fusion. Here's a step-by-step explanation:

1. The Sun's core is extremely hot and dense. This environment is perfect for nuclear fusion, a process where atomic nuclei combine to form a heavier nucleus.

2. In the Sun's core, hydrogen nuclei (protons) come together under high pressure and temperature.

3. Two protons combine to form a deuterium nucleus (one proton and one neutron), a positron (a positively charged electron), and a neutrino.

4. The deuterium nucleus then combines with another proton to form a helium-3 nucleus (two protons and one neutron).

5. Two helium-3 nuclei then combine to form a helium-4 nucleus (two protons and two neutrons) and two protons.

6. This process releases a large amount of energy in the form of light and heat. This energy travels to the Sun's surface and is emitted as sunlight.

7. The two protons released in the final step can then participate in further fusion reactions, continuing the cycle.

This process is known as the proton-proton chain reaction, and it's the primary source of the Sun's energy.