The correct answer is Option (4) → (B) and (C) only
To determine which statements regarding the rate of a chemical reaction are correct, let's analyze each one individually:
- (A) The rate of reaction is always proportional to the concentration of reactants: Incorrect. While true for many reactions (like first or second order), it is not always true. In a zero-order reaction, the rate is independent of the concentration of the reactants.
- (B) An exponential time course is followed by the first order reaction: Correct. For a first-order reaction ($A \rightarrow \text{Products}$), the integrated rate law is $[A] = [A]_0 e^{-kt}$. This means the concentration decreases exponentially over time.
- (C) The unit of rate of reaction in the gaseous state is atm s$^{-1}$: Correct. The rate of reaction is defined as the change in concentration (or pressure) per unit time. For gases, concentration is often expressed as partial pressure (atm), so the rate unit is atm/s or atm s$^{-1}$.
- (D) The concentration of reactant decreases exponentially with time for a zero order reaction: Incorrect. In a zero-order reaction, the concentration decreases linearly with time according to the equation $[A] = [A]_0 - kt$. It is the first-order reaction that follows an exponential decrease.
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