The mixture of the three substances can be seperated using water. Salt is the only substance which dissolves completely in water Pepper does not dissolve and is suspended on the surface or present as a suspension. Pebbles do not dissolve either and sink in water. When we dissolve this mixture in water, the pebbles settle down at the bottom and can be seperated mechanically. The pepper stays in suspension and can be seperated by filtration. The salt which dissolves in the water can be recovered by evaporating the water. Solution The mixture of the three substances can be seperated using water. Salt is the only substance which dissolves completely in water Pepper does not dissolve and is suspended on the surface or present as a suspension. Pebbles do not dissolve either and sink in water. When we dissolve this mixture in water, the pebbles settle down at the bottom and can be seperated mechanically. The pepper stays in suspension and can be seperated by filtration. The salt which dissolves in the water can be recovered by evaporating the water..