Km Measures Enzyme-Substrate Affinity Steps:

• Km is the substrate concentration at half maximum velocity (Vmax); lower Km indicates higher enzyme affinity for the substrate.
• List Km values: A (4 × 10^{-3} mol dm^{-3}), B (1 × 10^{-3}), C (2 × 10^{-3}), D (1 × 10^{-4}).
• Identify the highest Km value, which corresponds to the lowest affinity.
• Select option A with the largest Km (4 × 10^{-3} mol dm^{-3}).

Why A is correct:

• The highest Km value means the enzyme requires the highest substrate concentration for half Vmax, indicating lowest affinity per Michaelis-Menten kinetics.

Why the others are wrong:

• B: Km (1 × 10^{-3}) is lower than A's, so higher affinity.
• C: Km (2 × 10^{-3}) is lower than A's, so higher affinity.
• D: Km (1 × 10^{-4}) is the lowest, so highest affinity.

Final answer: A