If Mg2+has 12 protons and 12 neutrons, what is its atomic number and mass number?
Atomic number: It is defined as the number of protons present in the atom of an element.
Mass number: It is defined as the sum of number of protons and neutrons present in the atom of an element.
The number of protons in Mg2+ = 12, number of neutrons = 12
Therefore, the atomic number = number of protons= 12.
Mass number = number of protons + number of neutrons
= 12 + 12 = 24.