Answer: -
HCl (aq) and KOH (aq)
Explanation: -
Neutralization reaction is a type of reaction in which an acid and base react together to give salt and water.
A neutralization reaction is a type of double displacement reaction as well.
So if KCl is the salt that is formed then K should come from one and Cl from another.
Hence KOH and HCl are the acid and base that would neutralize to give KCl.