In paper chromatography, which equation is used to determine the $R_f$ value?
- A$R_f = \dfrac{\text{distance travelled by solvent}}{\text{distance travelled by substance}}$
- B$R_f = \dfrac{\text{distance travelled by locating agent}}{\text{distance travelled by substance}}$
- C$R_f = \dfrac{\text{distance travelled by substance}}{\text{distance travelled by locating agent}}$
- D$R_f = \dfrac{\text{distance travelled by substance}}{\text{distance travelled by solvent}}$