From the following statement regarding the order of reaction, the statement that is not true is

For complex reaction, order is given by the fastest step

The correct answer is Option (4) → For complex reaction, order is given by the fastest step

• Order of reaction is an experimental quantity: Order cannot be determined directly from the balanced chemical equation. It is determined experimentally from rate law studies. Therefore, this statement is true.
• The order of a reaction can be zero or even a fraction: Reaction order may be zero, fractional, or even negative depending on the reaction mechanism. Therefore, this statement is true.
• Order of reaction is applicable to elementary reaction: For elementary reactions, the order is equal to the molecularity because the reaction occurs in a single step. Therefore, this statement is true.
• For complex reaction, order is given by the fastest step: In complex reactions, the overall rate is determined by the slowest step (rate-determining step), not the fastest step. Thus, this statement is incorrect.