An atom becomes a positive ion when it loses one or more electrons.
This process occurs because electrons carry a negative charge, and when they are removed from the atom, the overall charge of the atom becomes positive. Atoms are neutral when they have an equal number of protons (which are positively charged) and electrons. By losing electrons, the balance shifts, resulting in a positively charged ion, also known as a cation. In contrast, if an atom were to gain electrons, it would become a negative ion, or an anion. Therefore, the simple answer is that an atom must lose electrons to become a positive ion.