Match the LIST-I with LIST-II.
| LIST-I Parameters | LIST-II Definition |
| A. Rate of reaction | I. Rate of the reaction when the concentration of each of the reactant is unity |
| B. Rate constant | II. Change in concentration of reactant or product per unit time |
| C. Order of a reaction | III. Sum of the powers to which the concentration terms are raised in the rate law. |
| D. Molecularity | IV. Number of reacting species taking part in an elementary reaction |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A-II, B-I, C-III, D-IV
All four terms describe a reaction through its rate law. For a reaction aA + bB → products whose rate is found by experiment:
\( \displaystyle \text{Rate}=k\,[A]^x\,[B]^y \)
A. Rate of reaction — This matches II. Change in concentration of reactant or product per unit time. It is measured as the decrease in concentration of a reactant or the increase in concentration of a product, in mol L−1 s−1.
\( \displaystyle r_{av}=-\frac{\Delta[R]}{\Delta t}=+\frac{\Delta[P]}{\Delta t} \)
B. Rate constant — This matches I. Rate of the reaction when the concentration of each of the reactant is unity. Putting [A] = [B] = 1 mol L−1 in the rate law gives Rate = k, so k is also called the specific reaction rate.
C. Order of a reaction — This matches III. Sum of the powers to which the concentration terms are raised in the rate law. Here the order is x + y. It is found by experiment and can be zero or even a fraction.
D. Molecularity — This matches IV. Number of reacting species taking part in an elementary reaction. It applies only to an elementary step, must be a whole number (1, 2 or 3) and cannot be zero.
Shortcut: The pair A–II appears only in Option (1).