The correct answer is Option (4) → (A), (C) and (D) only
Analysis of the Statements
- (A) The order of a reaction can be zero or an integer: CORRECT. Order is an experimentally determined quantity. It can be zero, an integer, or even a fraction.
- (B) The molecularity of a reaction can be zero or an integer: INCORRECT. Molecularity refers to the number of reacting species that must collide simultaneously to bring about a chemical reaction. Therefore, it cannot be zero, nor can it be a non-integer (fractional).
- (C) The molecularity cannot be zero or fraction: CORRECT. As mentioned above, you cannot have "zero" molecules colliding to create a reaction, nor can half a molecule collide in a single elementary step. Molecularity is always a positive whole number (1, 2, or 3).
- (D) The order of a reaction is decided by the slowest step of the complex reaction: CORRECT. In a complex (multi-step) reaction, the overall rate of the reaction is determined by the slowest step, often called the Rate Determining Step (RDS). The order of the reaction is derived from the stoichiometry of this specific step.
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