TLC stands for thin layer chromatography. Here we use a stationary phase like silica and a mobile phase, the solvent. when an analyte is run over stationary phase, the solvent is chose in such a way that it is will run faster than analyte. Rf stands fir retention factor. Rf is the ratio of distance travelled by analyte to distance traveled by solvent. It can never be greater than one. In the given question: Rf= 4.70cm/ 10 cm= 0.470 Thus it is a unit less term.