You're asking about a very important process in the Sun: nuclear fusion. To answer your question, we need to know the specific nuclear reaction you're talking about.

Here's why:

* The Sun's Primary Fusion Reaction: The most common reaction in the Sun is the proton-proton chain. This process involves four protons (hydrogen nuclei) combining to form one helium nucleus, releasing energy in the process.

* Other Fusion Reactions: The Sun also has other fusion reactions occurring, involving isotopes of hydrogen (deuterium and tritium), and even heavier elements like carbon and nitrogen.

To determine the atomic number and mass of the element formed, we need to know the specific reaction. Let me know the reaction, and I can tell you the resulting element!

For example, let's say the reaction is:

4 protons (⁴¹H) → ⁴₂He + 2 positrons + 2 neutrinos

Here's how we figure out the atomic number and mass:

* Atomic Number: The number of protons defines the element. Helium has 2 protons, so its atomic number is 2.

* Mass Number: The mass number is the total number of protons and neutrons. In this reaction, 4 protons combine to form a helium nucleus with 2 protons and 2 neutrons, giving it a mass number of 4.