Final answer:
When making carbon through nuclear fusion, three helium nuclei fuse together. The collision between two helium nuclei is not stable, so three helium nuclei are required to form a stable carbon nucleus. The temperature required for this fusion process is 100 million K.
Step-by-step explanation:
When making carbon through nuclear fusion, three helium nuclei fuse together. It takes three helium nuclei coming together simultaneously to make a stable nuclear structure because the product of a collision between two helium nuclei is not stable and falls apart quickly. Due to the repulsion between protons, it requires a temperature of 100 million K for three helium nuclei (six protons) to stick together and form a carbon nucleus.