Question

which is the first step in the fusion process?

Explanation:

In the proton - proton chain reaction which is the main fusion process in stars like the Sun, the first step involves two protons fusing to form a deuteron along with the emission of a positron and a neutrino. The third image shows two protons fusing to form a deuteron, a positron and a neutrino which is the first step in the fusion process.

Answer:

The third image (with Protons fusing to form Deuteron, Positron and Neutrino)