Answer:
hydrochloric acid
Explanation:
The hydrochloric acid in this reaction is the limiting reactant. A limiting reactant is the reactant that is used up in a chemical reaction. It determines the extent of the reaction.
Since the solution indicates a basic one after the end of the reaction, this suggests that more of the sodium hydroxide is still left unreacted with.
The reactant in excess supply here is the sodium hydroxide and the bulk of it is till left in solution.