Which conditions are necessary for fusion to occur?

For fusion, high temperature is the necessary condition.

High temperature gives hydrogen atoms enough energy to overcome the electrical repulsion between the atoms. This fusion process requires high temperature that is nearly about 100 million Kelvin and this temperature is six times hotter than the Sun's core. This high temperature provides enough energy to hydrogen atoms that they can overcome the electrical repulsion.

- "the choice that is not an indicator of a chemical change is "state of matter changes". more common than not, chemical reactions produce energy in the form of light or heat. along with energy, they also produce a new substance called the product that could be in any state of matter (solid, gas, or liquid)."