Final answer:
In thin-layer chromatography, an Rf value of 0.5 signifies that the substance traveled halfway from its starting point to the solvent front.
Step-by-step explanation:
An Rf value of 0.5 in thin-layer chromatography indicates the ratio of the distance traveled by the substance to the distance traveled by the solvent front. This Rf value means that the substance has moved half the distance from its original spot to the solvent front. If the solvent front traveled 10 cm, for instance, a substance with an Rf value of 0.5 would have traveled 5 cm. The Rf value is significant in identifying compounds since different substances tend to have different Rf values under the same chromatographic conditions.