Explanation:

Inadvertent and deliberate discharge of petroleum, improper sewage disposal, and thermal pollution also are seriously affecting the quality of the hydrosphere. The present discussion focuses on three major problems—eutrophication, acid rain, and the buildup of the so-called greenhouse gases. Only the water available at the surface of the ocean is involved in evaporation. In the hydrosphere, ocean water unsuitable for human use is 97%. Hence option 4th is correct.