In a nuclear reaction energy is released by the combination of two elements into a new element this process is an example of

Despite there being no answers listed by you, which the problem seems to be a multiple choice type of question, I'll go ahead and take a stab here.

What this problem is describing is basic nuclear fusion. Nuclear fusion is the process of which energy is released by a combination of two elements after they form into a brand new element. Once this happens, the bonded atoms have formed into a new, heavier nucleus.