Ions can be atomic or molecular. If an atom contains either positive or negative charge it said to be atomic cation or atomic anion.
When a molecule carry positive or negative charge it is called as polyatomic cation or polyatomic anion. Generally charged or ionized molecules are called as polyatomic ions.
In given question Fe(HCO₃)₃ ionizes as follow,
Fe(HCO₃)₃ → Fe³⁺ + 3 HCO₃⁻
The Ions produced are Fe³⁺ and HCO₃⁻. Fe³⁺ is said to be atomic (Ferric) ion and HCO₃⁻ (Bicarbonate) is polyatomic ion or molecular ion.
