Here's why:

* Plumbic refers to the +4 oxidation state of lead (Pb).

* Ions are atoms or groups of atoms that have gained or lost electrons, resulting in a net positive or negative charge.

* Since plumbic indicates a +4 oxidation state, the ion has lost four electrons, leaving a net positive charge of +4.

Therefore, the formula for the plumbic ion is Pb⁴⁺.