Write a net ionic equation for the overall reaction that occurs when aqueous solutions of sodium hydroxide and carbonic acid are combined. Assume excess base.
For equivalent amounts it will be
2NaOH + H2CO3 ==> Na2CO3 + 2H2O is molecular equation.
2Na^+(aq) + 2OH^-(aq) + H2CO3(aq) ==> 2Na^+(aq) + [CO3]^2-(aq) + 2H2O(l) is net ionic equation.
If you have excess NaOH added then there will be OH^-(aq) added on the right.