Given, an organic compound moved by $3.5 \mathrm{cm}$

Solvent moved by $5 \mathrm{cm}$

The R_f (retardation factor) value is the ratio of the solute’s distance travelled to the solvent’s distance travelled.

Retardation factor $=\frac{\begin{array}{c}\mathrm{Distance} \mathrm{travelled} \mathrm{by}\\ \mathrm{sample}/\mathrm{organic} \mathrm{compound}\end{array}}{\mathrm{Distance} \mathrm{travelled} \mathrm{by} \mathrm{solvent}}$

By putting the values in the above formula,

$$\begin{gathered} {\mathrm{R}}_{\mathrm{f}}=\frac{3.5}{5} \\ =7\times {10}^{-1} \end{gathered}$$