The correct answer is Option (4) → (A), (B) and (C) only
Analysis of the Statements
- (A) The order of a reaction is the sum of powers of the concentration of the reactants: TRUE. For a rate law expressed as $Rate = k[A]^x[B]^y$, the order is $x + y$. It describes how the reaction rate is affected by the concentration of reactants.
- (B) The order of a reaction may be zero, an integer or a fractional value: TRUE. Because order is determined experimentally, it can be $0$ (rate is independent of concentration), $1$, $2$, or even fractions like $1.5$.
- (C) Molecularity of an elementary reaction is equal to the number of reacting species: TRUE. Molecularity refers to the number of atoms, ions, or molecules that must collide simultaneously to bring about a chemical reaction.
- (D) The molecularity of a reaction may be zero or a fractional value: FALSE. Molecularity cannot be zero because a reaction cannot occur without at least one reactant molecule. Similarly, it cannot be a fraction because you cannot have half a molecule colliding in an elementary step. It is always a positive integer (1, 2, or 3).
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