* Identify the element: An atom with 21 protons is scandium (Sc).
* Determine the number of electrons: Neutral scandium has 21 electrons (equal to the number of protons).
* Consider the ionic form: The question doesn't specify the ionic form, so we need to consider the common possibilities:
* Sc³⁺: Scandium commonly forms a +3 ion by losing three electrons, leaving it with 18 electrons (21 protons - 3 electrons = +3 charge).
* Other possibilities: While less common, scandium can form other ions like Sc²⁺.
Therefore, the ionic charge of an ion with 21 protons could be +3 (Sc³⁺), but other charges are possible depending on the specific ionic form.
