Answer: The stronger conjugate base is, Citric acid.
Explanation :
The value of dissociation constant of Benzoic acid is higher than the citric acid. This means that the acid will readily dissociate and stronger will be the acid. Higher the value of dissociation constant of an acid weaker will be its conjugate base and the lower value of dissociation constant of an acid means that the stronger will be its conjugate base.
Therefore, the stronger conjugate base is Citric acid.