Water has a high dielectric constant. (It is able to break the ionic bonds between the ionic compounds. Eg: It separates the Na^+ and Cl^- ions of NaCl.) Hence it is a polar covalet compound and able to dissolve ionic compounds easily.
Whereas Benzene lacks the proper dielectric constant as water and hence can only dissolve a few substances (Such as Rubber).
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As water is a polar covalent compound it decreases the electrostatic forces of attraction , resulting the free ions in the aqueous solution