Under what conditions are the concentrations of Fe3+(aq) and Fe2+(aq) measured when determining their potential?

The correct choice focuses on the standard conditions typically used for measuring the potential of half-cells in electrochemistry. Standard conditions are defined to provide a consistent basis for comparison of electrochemical data.

At 298 K (which is equivalent to 25°C), the standard state is conventionally considered, and a concentration of 1 mol dm⁻³ is commonly used for solutions when calculating standard electrode potentials. These conditions are significant because they reflect a standard reference that allows for the comparability of electrochemical measurements across different systems.

In this context, measuring the concentrations of Fe³⁺ and Fe²⁺ at 1 mol dm⁻³ under standard temperature (298 K) shows the typical conditions under which standard potentials are established. This reflects the way electrochemical cells are standardized in a laboratory setting to ensure reproducibility and accuracy in experimental results.

Other choices introduce variations either in temperature or concentration that deviate from the standard conditions, which would hinder direct comparison with standard electrochemical potential tables or measurements.