The correct choice is (c) Kcat/Km
To explain I would say: Kcat/Km is termed as catalytic efficiency. A high value indicates that the limiting factor of the overall reaction is the collision frequencies between enzyme and substrate molecule, whereas the low value indicates the equilibrium assumption status. Km and Kcat represent the Miachelis Menten constant and turn over number respectively. Vmax is the maximum rate of the reaction catalyzed by enzymes.