Consider the following statements about the way chemical reactions take place.
(A) Reactions taking place in one step are called elementary reactions.
(B) The nitration of phenol, which yields o-nitrophenol and p-nitrophenol, is an example of reverse reactions.
(C) A balanced chemical equation does not give a true picture of how a reaction takes place, since rarely a reaction gets completed in one step.
(D) The sequence of elementary reactions that gives the products of a complex reaction is called its rate law.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (B) and (D) only
Most reactions do not happen in the single step their balanced equation suggests. A reaction may go through a series of simple steps, and the products may be formed by more than one route.
(A) Reactions taking place in one step are called elementary reactions. — Correct statement. A one-step reaction is an elementary reaction.
(B) The nitration of phenol, which yields o-nitrophenol and p-nitrophenol, is an example of reverse reactions. — Incorrect statement. Phenol gives two products at the same time, so this is an example of side reactions. Reverse reactions are those in which the products change back into the reactants.
(C) A balanced chemical equation does not give a true picture of how a reaction takes place, since rarely a reaction gets completed in one step. — Correct statement. The equation shows only the starting substances and the final products, not the steps in between.
(D) The sequence of elementary reactions that gives the products of a complex reaction is called its rate law. — Incorrect statement. This sequence of steps is called the mechanism of the reaction. The rate law is the expression of the rate in terms of the concentrations of the reactants.
NCERT (2026-27 edition):
3.2.3 Order of a Reaction – “A balanced chemical equation never gives us a true picture of how a reaction takes place since rarely a reaction gets completed in one step. The reactions taking place in one step are called elementary reactions. When a sequence of elementary reactions (called mechanism) gives us the products, the reactions are called complex reactions. These may be consecutive reactions (e.g., oxidation of ethane to CO2 and H2O passes through a series of intermediate steps in which alcohol, aldehyde and acid are formed), reverse reactions and side reactions (e.g., nitration of phenol yields o-nitrophenol and p-nitrophenol).”