Answer: -
Sodium Benzoate is a salt. Sodium salts are ionic compounds.
Sodium benzoate is an ionic compound whereas benzoic acid is a covalent compound.
Ionic compounds dissolve in water while covalent compounds do not.
Similarly ionic compounds do not dissolve in non polar solvents but covalent compounds do.
It is because of this reason that sodium benzoate dissolve so well in water, whereas benzoic acid does not