Answer:
It is known generally that polar compounds are soluble in polar solvents. Based on the structure of benzoic acid, it comprises the non-polar C6H6 group and polar COOH group. Based on the structure, in benzoic acid, the nonpolar hydrocarbon outweighs and influences the polar part as nonpolar, due to which benzoic acid is not soluble in water.
On the other hand, benzoic acid produces sodium salt benzoic acid when it reacts with 2.5 M sodium hydroxide, this salt is ionic. Generally, the ionic compounds are soluble in water. Therefore, the salt of benzoic acid gets dissolved in water. Hence, benzoic acid is soluble in the solution of sodium hydroxide.