If you were told an atom was an ion, you would know the atom must have a
The atom must have gained 1 or more electrons or must have lost 1 or more electrons.
Explanation:
In an atom number of electrons and protons are equal. it is an electrically neutral specie.
In an ion, the number of electrons and protons are not equal. There are two types of an ion :
Hence, if an atom is considered as an ion, then it will have an unequal number of protons and electrons.