The correct option is A The acid has one more proton
According to Bronsted-lowry theory, an acid is an proton donor and a base is an proton acceptor. The strength of an acid/base depends upon extent upto which it can accept/donate proton. In bronsted acids and it's conjugate base with strong acid, the strength of the acid is very strong i.e it can donate a proton very easily but it's conjugate Is a weak base that cannot accept the proton merely. Similarly if the base is stronger then it's conjugate acid will be a weak acid, therefore there exist a interrelationship between acids and it's conjugate bases and vice versa.