Which of the following statements is correct?
- AA mixture of liquids with boiling points which differ by $35\,^{\circ}\text{C}$ can be separated by distillation.
- BLocating agents are needed to identify the colours present in ink.
- CThe desalination of sea water to produce pure water is achieved by fractional distillation.
- DThe $R_f$ value of a dye in a chromatogram can be calculated using the formula: $R_f = \frac{\text{distance moved by solvent}}{\text{distance moved by spot}}$