Na₂CO₃ or Sodium carbonate is actually washing soda. When it is stirred in water, it dissociates into 2 types of ions.
The cation (positive ion) is monovalent cation sodium ion- Na⁺
and anion (negative ion) is divalent anion carbonate ion (a polyatomic ion) CO₃²⁻
Therefore, it can be written as:-
Na₂CO₃------------> 2Na⁺ CO₃²⁻
So, for every carbonate ion, there are 2 sodium ions.