Which of the following statements are correct: (i) law of mass action and rate law expressions - are same for single step reaction
(ii) the slowest step of a complex reaction gives the order of the complex reaction
(iii) both order and molecularity have normally a maximum value of 3
(iv) m olecularity of a com plex reaction `A + 2B to C` is 3

Options

A. I,ii,iii
B. All are correct
C. ii,iv
D. ii,iii,iv

Explanation

To determine which of the statements regarding chemical kinetics are correct, we will analyze each statement one by one.

### Step 1: Analyze Statement (i)
**Statement:** Law of mass action and rate law expressions are the same for single step reactions.

**Analysis:**
For a single-step reaction, the law of mass action states that the rate of the reaction is proportional to the product of the active masses (concentrations) of the reactants. This is indeed the same as the rate law expression for that reaction. Therefore, this statement is **correct**.

### Step 2: Analyze Statement (ii)
**Statement:** The slowest step of a complex reaction gives the order of the complex reaction.

**Analysis:**
In a complex reaction, the rate-determining step (the slowest step) dictates the overall rate of the reaction. The order of the reaction can be determined from the rate law of this slowest step. Hence, this statement is also **correct**.

### Step 3: Analyze Statement (iii)
**Statement:** Both order and molecularity have normally a maximum value of 3.

**Analysis:**
Molecularity refers to the number of reactant particles involved in an elementary reaction, and it is true that for elementary reactions, the maximum molecularity is typically 3. However, the order of a reaction can be greater than 3 in complex reactions. Therefore, this statement is **incorrect**.

### Step 4: Analyze Statement (iv)
**Statement:** Molecularity of a complex reaction `A + 2B → C` is 3.

**Analysis:**
Molecularity is defined for elementary reactions and refers to the number of molecules that collide to produce the reaction. For the reaction `A + 2B → C`, if we consider it as a single elementary step, its molecularity would indeed be 3. However, for complex reactions, molecularity is not typically defined in the same way. Therefore, this statement is **incorrect**.

### Final Conclusion:
The correct statements are:
1. Statement (i) is correct.
2. Statement (ii) is correct.
3. Statement (iii) is incorrect.
4. Statement (iv) is incorrect.

Thus, the correct statements are **(i) and (ii)**.

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