For the elementary reaction X + Y → Products, the rate equation is Rate = k[X][Y]. Consider the following statements in this regard:
(A) The order of the reaction is one.
(B) The molecularity of the reaction is two.
(C) The rate constant depends upon the temperature.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (B) and (C) only
The order of a reaction is the sum of the powers of the concentration terms in the rate law. The molecularity of an elementary reaction is the number of reacting species that must collide at the same time for the reaction to occur.
(A) The order of the reaction is one. — False. In Rate = k[X]1[Y]1 the powers are 1 and 1, so the order is 1 + 1 = 2. The reaction is first order in X and first order in Y, but its order is two.
(B) The molecularity of the reaction is two. — True. The reaction is elementary, and one X and one Y collide in it, so it is bimolecular.
(C) The rate constant depends upon the temperature. — True. k changes with temperature; for a 10° rise it is nearly doubled.
NCERT (2026-27 edition):
3.2.3 Order of a Reaction – “… the sum of powers of the concentration of the reactants in the rate law expression is called the order of that chemical reaction.”
3.2.4 Molecularity of a Reaction – “… The number of reacting species (atoms, ions or molecules) taking part in an elementary reaction, which must collide simultaneously in order to bring about a chemical reaction is called molecularity of a reaction. … Bimolecular reactions involve simultaneous collision between two species, for example, dissociation of hydrogen iodide.”
3.4 Temperature Dependence of the Rate of a Reaction – “It has been found that for a chemical reaction with rise in temperature by 10°, the rate constant is nearly doubled.”