So it's 58Fe2- ?

Answer 1

Look in the periodic table and find iron (Fe). It has an atomic # = 26 and atomic mass 56.

Protons = 26

Electrons = 26

Neutrons = 56 - 26 = 30 neutrons

For ^58Fe, the atomic mass is 58, but it still has 26 protons. So, number of neutrons = 58-26 = 32 neutrons

For ⁵⁸Fe^2-, the atomic mass is 58, it has 26 protons, but now it 28 electrons (2- charge). Neutrons is 32.