Why is it rare to find a 4 plus ion of carbon?
It is rare to find a 4 plus ion of carbon because of the increasing energy required to ionize carbon. Ionization energy increases with each time.
If I interpret your question correctly, C is the element Carbon. When followed by a plus (in speaking) or a plus symbol it means it has a charge of one unit (elementary charge - charge on one electron). Because Carbon is defined as an atom with 6 protons, this means the Carbon in question must have 5 electrons. Thus it is an ion.
Carbon has an oxidation number of +4 in both carbonate and bicarbonate. Oxygen as usual has an oxidation number of -2, and hydrogen has an oxidation number of +1. Therefore, the ion CO3-2 has six negative charges from oxygen partly balanced by four positive changes from carbon for a net of -2, and HCO3-1 has six negative charges from oxygen partly balanced by one positive from hydrogen and needs for plus four from carbon for…