Why must the starting line on which the spot of food colouring was placed be above the level of solvent?

The starting line for the spot of food coloring must be above the level of the solvent to prevent the dye from dissolving into the solvent immediately. If the spot is submerged, the coloring would disperse too quickly, leading to poor separation and making it difficult to observe the distinct movement of the dye. Keeping it above allows the dye to travel with the solvent front as it moves up the paper, enabling better analysis of its properties.