When an ion is formed, the number of protons does not change. By removing an electron from this atom we get a positively charged Na+ ion that has a net charge of +1. Atoms that gain extra electrons become negatively charged. A neutral chlorine atom, for example, contains 17 protons and 17 electrons
4% mass / volume :
4 g ---------> 100 mL
1.2 g ------- ? mL
V = 1.2 * 100 / 4
V = 120 / 4
V = 30 mL
hope this helps!
Atomic mass. Which is the number of protons and neutrons combined.