Describe the protons, electrons, and neutrons of an atom of hydrogen-2.

However, various hydrogen isotopes, such as H-2, have one proton and one neutron; H-3 has one proton and two neutrons, etc. The sum of the protons and neutrons in an atom's nucleus is its atomic mass. Thus, the atomic mass of the H-2 isotope is two, the atomic mass of the H-3 isotope is three, and so forth.

Explanation:

it's c. elements are placed in rows based on how may valencies electrons have.