Final answer:
Without specific experimental data showing the effects of various concentrations of cadmium on leaf size, it is not possible to determine which concentration had the largest effect on leaf size.
Step-by-step explanation:
To discern at which concentration of cadmium the largest effect on leaf size was observed, there must be data presented in the form of a study or experiment where different concentrations of cadmium are tested on plant leaf size. However, within the context provided, no specific data relating to concentrations of cadmium and their effects on leaf size are mentioned. Therefore, it's impossible to accurately determine the answer to this question without additional experimental data or results.
Typically, such an experiment would involve growing plants under different concentrations of cadmium and measuring the leaf sizes to draw a conclusion. Higher concentrations of cadmium are likely to lead to more significant reductions in leaf size, due to cadmium's toxic effects on plant growth, but the exact concentration that causes the largest effect would be based on empirical evidence.