# How many protons would a positively charged isotope ions of O-18 have?

It would have $8$ protons.
Elements are distinguished by the number of protons in their nucleus. This number is called the atomic number, and for Oxygen, it is $8$.
Thus, any atom of Oxygen, whether positive or negative, will have $8$ protons. If it is positively charged, this simply means that it has $< 8$ electrons such that the net charge is positive.