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. Molecularity of the slowest elementary step of a complex reaction gives molecularity of reaction
C. Both order and molecularity have a value of 2 commonly
D. Molecularity of a complex reaction A + 2B`to`C with certainty

Answer

To determine which statement is not correct, we will analyze each of the provided statements step by step.

### Step 1: Analyze Statement A
**Statement A:** "The law of mass action and rate law expression are the same for step reactions."

- **Explanation:** Step reactions, also known as elementary reactions, have a direct relationship between the rate of reaction and the concentrations of the reactants. According to the law of mass action, the rate of a reaction is proportional to the concentration of the reactants raised to the power of their coefficients in the balanced equation. Therefore, this statement is **true**.

### Step 2: Analyze Statement B
**Statement B:** "The order of the slowest elementary reaction of a complex reaction gives the order of the complex reaction."

- **Explanation:** In a complex reaction, the rate-determining step (which is the slowest step) dictates the overall rate of the reaction. The order of the overall reaction is indeed determined by the slowest step. Thus, this statement is also **true**.

### Step 3: Analyze Statement C
**Statement C:** "Both order and molecularity have normally a maximum value of 3."

- **Explanation:** Molecularity refers to the number of reactant particles involved in an elementary reaction, and it can only be a whole number (1, 2, or 3). However, the order of a reaction can be any non-negative integer or even a fraction, and it can exceed 3. Therefore, this statement is **false**.

### Step 4: Analyze Statement D
**Statement D:** "The molecularity of a complex reaction A + 2B gives C is 3."

- **Explanation:** In the reaction A + 2B → C, the molecularity is calculated by summing the number of reactant molecules involved, which is 1 (for A) + 2 (for B) = 3. This statement is **true**.

### Conclusion
After analyzing all the statements, we find that the statement that is not correct is **Statement C**.

### Final Answer
The statement that is not correct is Statement C: "Both order and molecularity have normally a maximum value of 3."

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