A reaction proceeds by the following three-step mechanism:
Step 1 A → B ΔH₁ = +25 kJ
Step 2 B → C ΔH₂ = −90 kJ
Step 3 C → D ΔH₃ = +10 kJ
Which statement best describes the qualitative shape of the overall energy profile for the reaction?
a) It contains two transition states and two intermediates, with products higher in energy than reactants.
b) It shows three energy minima that correspond to transition states, and the reaction is overall exothermic.
c) It contains three transition states and two intermediates, with products lower in energy than reactants.
d) It contains three transition states and two intermediates, with products higher in energy than reactants.