Use the group number to determine the charge on an ion derived from each element.
Rubidium,
Aluminum,
Phosphorus,
Bromine:
Rubidium (Rb) belongs to group 1 which means it will have a charge of +1 on its ion.
Aluminum (Al) belongs to group 3 which means it will have a charge of +3 on its ion.
Phosphorus (P) belongs to group 15 which means it will have a charge of -3 on its ion.
Bromine (Br) belongs to group 17 which means it will have a charge of -1 on its ion.