Question

which is the third step in the fusion process?

Explanation:

In the proton - proton chain reaction (a common fusion process in stars), the first step is two protons fusing to form a deuteron along with a positron and a neutrino. The second step involves a deuteron fusing with a proton to form helium - 3. The third step is two helium - 3 nuclei fusing to form helium - 4 and two protons. The middle diagram shows two helium - 3 nuclei fusing to form helium - 4, which is the third step.

Answer:

The middle diagram (showing helium - 3 fusing to form helium - 4)