A paper chromatograph of four dyes, G, P, R and Y, is shown below - VCE - SSCE Chemistry - Question 4 - 2016 - Paper 1

To determine the Rf value, we use the formula:
$Rf = \frac{d_{dye}}{d_{solvent}}$
where $d_{dye}$ is the distance traveled by the dye from the origin to the center of the dye spot and $d_{solvent}$ is the distance from the origin to the solvent front.

Looking at the chromatogram:

• For the dye with the lowest position corresponding closely to the origin indicates it is the most strongly adsorbed. In this case, the dye G appears to be this one.
• If we estimate the distance for G to be around 5 units and the solvent front at 20 units, we can calculate:
  $Rf_{G} = \frac{5}{20} = 0.25$

Thus, the dye most strongly adsorbed onto the stationary phase has an Rf value of 0.25, corresponding to option A.