Km is substrate concentration at half maximum velocity (Vmax/2)

Steps:

• Identify Vmax as the plateau rate on the graph.
• Compute half Vmax (Vmax/2).
• Locate substrate concentration [S] where reaction rate equals Vmax/2.
• This [S] value is Km, reading 1.5 mmol dm⁻³ from the graph.

Why C is correct:

• Km is defined as [S] at which velocity is Vmax/2 in Michaelis-Menten kinetics.

Why the others are wrong:

• A and B: Substrate concentrations below Vmax/2 point, underestimating Km.
• D: Substrate concentration above Vmax/2 point, overestimating Km.

Final answer: C