Answer: B (The Rf value would decrease)
Step-by-step explanation:
The Rf (retention factor) value is a ratio of the distance traveled by the compound to the distance traveled by the solvent front in thin-layer chromatography (TLC). The polarity of the solvent affects the Rf value of a compound.
In general, if a more polar solvent is used in TLC, the Rf value of a compound will decrease, and if a less polar solvent is used, the Rf value will increase.
In this case, using 40% ethyl acetate in hexanes means using a more polar solvent compared to a pure hexanes solvent. As eugenol is a moderately polar compound, the increased polarity of the solvent will likely result in a decrease in the Rf value.
Therefore, the correct answer is b. The Rf value would decrease.