Which of the following statements is not correct ?

Options

A. Law of mass action and rate law expressions are same for single -step reactions .
B. Order of the slowest elementray reaction of a complex reaction gives the order of the complex reaction .
C. Both oder and molecularity have normally a maximum value of 3.
D. Molecularity of a complex reaction `A+2B to C` is 3 .

Answer

To determine which of the statements is not correct, let's analyze each statement one by one based on the principles of chemical kinetics and equilibrium.

### Step 1: Analyze the first statement
**Statement:** "Law of mass action and rate law expression are the same for single step reactions."

**Analysis:** This statement is correct. For single-step reactions, the rate law expression can be derived directly from the stoichiometry of the reaction, which is also applicable in the law of mass action at equilibrium.

### Step 2: Analyze the second statement
**Statement:** "Order of the slowest elementary reaction of a complex reaction gives the order of the complex reaction."

**Analysis:** This statement is also correct. The overall order of a complex reaction is determined by the slowest step (rate-determining step) in the reaction mechanism.

### Step 3: Analyze the third statement
**Statement:** "Both order and molecularity have a maximum value of 3."

**Analysis:** This statement is incorrect. Molecularity, which refers to the number of reactant molecules involved in an elementary reaction, can have a maximum value of 3 (unimolecular, bimolecular, and termolecular). However, the order of a reaction can be any non-negative integer and is not limited to a maximum value of 3; it can be infinite depending on the reaction mechanism.

### Step 4: Analyze the fourth statement
**Statement:** "Molecularity of a complex reaction is 3."

**Analysis:** This statement is correct. If a complex reaction has a rate-determining step with a stoichiometry that sums to 3, then its molecularity can indeed be 3.

### Conclusion
After analyzing all statements, the statement that is not correct is the third one: "Both order and molecularity have a maximum value of 3."

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