Answer:There are two kind of nuclear ractions: fusion and fission reactions.
Both release a huge amount of energy in different ways.
Fusion reactions are nuclear reations in which two smaller (lighter) atoms combine into a larger (heavier) atom, with the respective release of energy.
That is what model 1 shows:
Model 1: Atom 1 + Atom 2 = Atom 3 + energy
That is the process that happens and is responsible for the huge amount of heat produced in and released by the Sun.
In the Sun two atoms of hydrogen fuse into a larger atom of helium.
That is represented by the nuclear reaction:
Explanation: