Question

How would adding the catalyst nitrogen monoxide (NO) affect this reaction?

Answer 1

If nitrogen monoxide (NO) is added to 2SO2(g) + O2(g) → 2SO3(g),

it will react with O2 and decrease the reaction rate by lowering the amount of O2.  So the answer is C.  NO decreases collisions between the SO2 and O2 molecules.

Answer 2

Answer: A.  NO increases the rate at which $SO_3$ molecules are formed.

Explanation: The catalyst makes it possible for the reaction to take place by another path that makes possible reaction at a lower energy.

Activation energy is the extra energy that must be supplied to reactants in order to cross the energy barrier and thus convert to products.

A catalyst is a substance which increases the rate of a reaction by taking the reaction through a different path which involves lower activation energy and thus more reactants $(SO_2)$ and $(O_2)$ undergo collision and can cross the energy barrier and convert to products $(SO_3)$

Thus NO increases the rate at which $SO_3$ molecules are formed.