The charge of an ion is a function of the number of protons and electrons in the atom.
An atom consists of three subatomic particles namely: neutron, proton and electron. The proton is positively charged while the electron is negatively charged.
The charge of an atom is determined by subtracting the number of electrons from protons, that is;
Charge = no. of protons - no. of electrons
Hence, if the protons in an atom is more than the electrons, the charge will be positive and vice versa. In this case, an element has 20 protons, 22 neutrons and 18 electrons.
Therefore, the charge of the ion will be 20 protons - 18 electrons = +2
