Concept:Saturation occurs when the remaining water can hold at most 25 gm of salt per 100 gm of water.Explanation:Total mass of solution =1 kg =1000 gm.Salt in 4% solution =1000×1004​=40 gm.Initial water in the solution =1000−40=960 gm.For 40 gm of salt, minimum water needed before sedimentation starts is 2540​×100=160 gm.Water to be evaporated =960−160=800 gm.Evaporation rate =28 gm/hour.Required time =28800​=28.57 hours, approximately.Therefore, sedimentation starts after about 29 hours.Answer:A. 29 h