ANS:B - exponentially

For a first-order chemical reaction, the concentration of the reactant decreases exponentially with time. In a first-order reaction, the rate of the reaction is directly proportional to the concentration of the reactant. Mathematically, the rate of decrease in concentration (d[A/dt ]​) of the reactant over time (t) is expressed by the first-order rate law: d[A]/dt ​=−k[A] where:

• d[A]/dt ​ is the rate of change of the concentration of the reactant over time,
• k is the rate constant of the reaction,
• [A] is the concentration of the reactant.

• [A]0​ is the initial concentration of the reactant,
• e is the base of the natural logarithm,
• k is the rate constant,
• t is time.