In the given situation, the reaction is-
NO + H2 ↔ Products
The rate of the reaction can be expressed (in terms of the decrease in the concentration of the reactants) as-
Rate = -dΔ[NO]/dt = -dΔ[H2]/dt
Now, if the concentration of NO is decreased there will be fewer molecules of the reactant NO which would decrease the its collision with H2. As a result the rate of the forward reaction would also decrease.
Ans) A decrease in the concentration of nitrogen monoxide decreases the collisions between NO and H2 molecules. the rate of the forward reaction then decreases.
