Select the correct statement(s) :

Options

A. Every substance tht appears in the rate law of reaction must be a reactant or product in that reaction
B. If we know the rate law of a reaction , we can deduce its mechanism
C. If the reaction has rate `r=k[A][B]^(3//2)` then reaction may be elementary
D. A zero order reaction must be a complex reaction

Answer

To solve the question regarding the correct statements related to chemical kinetics, let's analyze the information provided in the video transcript step by step.

### Step 1: Understanding Rate Laws
The transcript mentions that "Every substrate that appears in the rate law of reaction must be a reactant or product in that reaction." However, it also states that "Every substrate that appears in the rate law of reaction might not be a reactant or a product because sometimes catalyst intermediate appears in the rate law."

**Conclusion:** This statement is incorrect because intermediates can appear in the rate law without being reactants or products.

**Hint:** Consider the role of intermediates and catalysts in chemical reactions and how they relate to the rate law.

### Step 2: Deducing Mechanisms from Rate Laws
The transcript states, "if we know the rate law of a reaction, we can deduce its mechanism." However, it also clarifies that "we cannot be sure of its mechanism unless we have some other evidence about the intermediate forms."

**Conclusion:** This statement is partially correct. While the rate law can provide insights into the mechanism, it is not definitive without additional evidence.

**Hint:** Think about the difference between deducing a mechanism and confirming it.

### Step 3: Elementary vs. Complex Reactions
The transcript discusses that "if the reaction has rate this then the reaction may be elementary." It further states that "it can be elementary," meaning that not all reactions with a certain rate law are elementary.

**Conclusion:** This statement is correct. Reactions can be elementary or complex, and the presence of a rate law does not guarantee that a reaction is elementary.

**Hint:** Recall the definitions of elementary and complex reactions and their characteristics.

### Step 4: Zero-Order Reactions
The transcript mentions, "A zero-order reaction must be a complex reaction." This is a crucial point because zero-order reactions can occur under specific conditions and do not necessarily indicate complexity.

**Conclusion:** This statement is incorrect. Zero-order reactions can be elementary and do not have to be complex.

**Hint:** Review the characteristics of zero-order reactions and their relation to reaction mechanisms.

### Step 5: Molecularity and Order of Reactions
The transcript states, "Molecularity and order of a reaction both are equal for elementary reactions." This is true because, for elementary reactions, the molecularity (the number of molecules involved in the reaction) is equal to the order of the reaction.

**Conclusion:** This statement is correct.

**Hint:** Understand the definitions of molecularity and order, and how they apply to different types of reactions.

### Final Summary of Correct Statements
Based on the analysis:
1. The statement about substrates in the rate law is incorrect.
2. The statement about deducing mechanisms from rate laws is partially correct.
3. The statement regarding elementary reactions is correct.
4. The statement about zero-order reactions being complex is incorrect.
5. The statement about molecularity and order being equal for elementary reactions is correct.

### Final Answer
The correct statements are:
- "If we know the rate law of a reaction, we cannot be sure of its mechanism unless we have some other evidence about the intermediate forms."
- "Molecularity and order of a reaction both are equal for elementary reactions."