On a 'which line' question that plots volume or mass of product against time, read the curve as two independent things: its final plateau and its initial steepness. They are set by different quantities, so decide each one separately.
Trigger: a graph comparing experiments, or an experiment described against a reference line P, on a product-versus-time plot.
Instances:
(i) the plateau height is fixed only by the moles of the limiting reagent: work out the moles of each reactant against the equation ratio, the smaller caps the product;
(ii) the initial steepness is fixed by the rate factors: concentration, surface area (powder faster than granules faster than a lump), temperature and catalyst;
(iii) a change that only affects rate (surface area, temperature, catalyst, mass of catalyst) leaves the plateau exactly where it was, so both curves finish at the same height;
(iv) for a 'produce this amount in the shortest time' question, first eliminate every option that cannot make that amount at all, then compare the rate of the survivors.
