Calculate the ${R_{\text{f}}}$ of the amino acid.

${R_{\text{f}}} = \frac{{40{\text{ (mm)}}}}{{46{\text{ (mm)}}}} = 0.87$;

Allow 0.86 to 0.88.

No mark if ${R_{\text{f}}}$ has units.

There were difficulties in the calculation of ${R_{\text{f}}}$, some candidates did not seem to know what it means, others what to measure.