Which one of the atoms shown would be most likely to form a cation with a charge of 1?

Ions are stable atoms of elements formed when original atoms loose or gain electrons to form stable configuration. Anions are negatively charged ions formed when atoms gain electrons while cations are the positively charged ions formed when atoms loose electrons. In this case a charge of + 1 means an atom lost one electron to form a stable configuration. Therefore, the correct answer is A