Rubidium-85 can turn into a rubidium ion with a charge of 1+ by losing one of its electrons. Since electrons have a negative charge of -1, removing one electron increases the overall positive charge of the atom by 1. This transforms it from the neutral rubidium-85 atom to a positively charged rubidium ion.

In the case of rubidium-85 specifically, it has a total of 37 electrons. In its neutral state, the number of positively charged protons in its nucleus is balanced by the 37 negatively charged electrons. To become an ion with 1 charge, it needs to lose one electron, leaving it with 36 electrons and 37 protons. Since the number of protons now exceeds the number of electrons by one, the atom has a net positive charge of +1, making it a rubidium-85 ion.

This process of losing an electron is typically the result of chemical reactions or interactions with external energy sources, such as heat or light, which provide enough energy to overcome the attractive force between the electron and the positively charged nucleus.