The correct reaction profile diagram for a positive catalyst reaction.

Solution

Chemistry ma’am · 3 steps

A positive catalyst lowers only the hump; the reactant and product levels must not move at all.

1. What a catalyst does. A positive catalyst gives the reaction a new pathway with a lower activation energy. So the dashed curve's peak must sit below the solid curve's peak.
2. What it cannot do. A catalyst does not change the energy of the reactants or the products. So Δ H stays the same, and both curves must start at one level and end at one level.

   Option	Peak with catalyst	Reactant and product levels	Verdict
   (a)	higher	products end at different places	wrong on both counts
   (b)	lower	product energy differs, so Δ H changes	wrong
   (c)	higher	same	negative catalyst
   (d)	lower	same	positive catalyst

3. So. Only (d) shows a lower peak with the catalyst while the reactant and product energies stay unchanged. The answer is (d).

The idea to keep. On any energy profile, a catalyst changes only the height of the barrier. If the start or end level moves, Δ H has changed, and no catalyst can do that.

Answer from the NTA final answer key. Solution by PrepWiser.