Answer
a) $Rb^{1+}$
b) $K^{1+}$
c) $Al^{3+}$
d) $O^{2-}$
Work Step by Step
a) and b) Since Rb and K are both Group 1 (Alkali Metals), they will form the positive cation with a +1 charge because in order to become stable they need to simply lose one electron to obey the octet rule which is possible by losing one electron.
c) Aluminum will form the ion +3 because it's in group 5, is a metal, and needs to lose 3 electrons to become stable. This can be achieved by losing 3 electrons.
d) Lastly, oxygen would become an anion by gaining two electrons since it's a non-metal, and since it's in group 6, it can gain 2 more electrons to have a full octet and thus can become stable.
