Consider the reaction A B. The concentration of both the reactants and the products varies exponentially with time. Which of the following figures correctly describes the change in concentration of reactants and products with time?

For a given reaction the concentration of A and B varies exponentially with time as given when the reaction will begin the concentration of A will be maximum and with the passage of time will reduce and moves towards zero with exponentially i.e. becoming asymptotic to the x-axis.

Similarly, the concentration of product B will increase exponentially with the passage of time and will become constant. Towards the completion of the reaction the concentration of product B will increase with a small rate as concentration of A on L.H.S has reduced significantly.

IMPORTANT FACT: L.H.S means Left hand side of reaction.