The elements shown in the answer have their common ions written beside them.
Silicon mostly forms positive ions in oxyacids and complex ions. Arsenic mostly forms its anion. Magnesium forms only the +2cation just as rubidium only forms the +1 cation. The fluoride ion is F^- while tin may for a +2*or +4 cation. Germanium usually forms the +4 cation.
This is true. Think about when you make pasta. The colander acts as a filter and doesn't let the past a through but allows the extra water to escape because the pasta is too big to fit.
