Which of the following statements are correct?
A. The overall rate of a reaction is controlled by the slowest step in a reaction.
B. Order of a reaction is an experimental quantity.
C. Molecularity is applicable to elementary as well as complex reactions.
D. The number of reacting species taking part in an elementary reaction is called molecularity of a reaction.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A, B and D only
Most reactions take place in a series of elementary steps, and the slowest step (the rate-determining step) controls the rate of the whole reaction. Order is found by experiment, while molecularity is defined only for an elementary reaction.
A. The overall rate of a reaction is controlled by the slowest step in a reaction. — Correct. The slowest step is the rate-determining step.
B. Order of a reaction is an experimental quantity. — Correct. It cannot be predicted from the balanced equation.
C. Molecularity is applicable to elementary as well as complex reactions. — Incorrect. Molecularity applies only to elementary reactions; for a complex reaction it has no meaning.
D. The number of reacting species taking part in an elementary reaction is called molecularity of a reaction. — Correct. This is the definition of molecularity.
NCERT (2026-27 edition):
Molecularity of a Reaction
