Includes a fully accurate, relevant diagram with correctly labelled curves (D=MPB, MSB, S₁=MPC, S₂=MPC+tax), axes, equilibrium and optimum points.

Clearly illustrates the tax wedge and supply shift, making the policy mechanism immediately understandable.

Labels key prices (Pₚ, Pₘ, P_c) and quantities (Qₒₚₜ, Qₘ) in line with IB expectations.

Minor labelling ambiguities (e.g. redundant S₁ labels) that could confuse readers if unchecked.

The caption omits explicit reference to the welfare‐loss triangle, which would strengthen the analytical link between diagram and text.

Appropriate economic terms (excise duty, negative externality, allocative inefficiency, social optimum) are used consistently.

Specialist notation (MPB, MSB) appears throughout the commentary in the correct context.

Occasional informal phrasing (e.g. “big economic cost”) that reduces academic precision.

Minor language errors (e.g. “overallocation of resources happen”) momentarily impede clarity.