Consider the following statements:
I) The value of rate constant is never negative
II) A zero order reaction is an elementary reaction
III). For elementary reactions, molecularity and order are equal
IV). Average and instantaneous rate of reaction are defined for micro and macroscopic time interval respectively The correct statement(s) is/are

Options

A. I, II, Ill
B. Only III
C. I, III
D. I, II, IV

Answer

To solve the question, we need to evaluate each of the provided statements regarding chemical kinetics and determine which ones are correct.

### Step-by-Step Solution:

1. **Statement I: The value of rate constant is never negative.**
- The rate constant (k) is a proportionality constant in the rate equation of a reaction. It relates the rate of reaction to the concentrations of the reactants. Since the rate of reaction cannot be negative (as it would imply a negative concentration change), the rate constant must also be non-negative.
- **Conclusion:** This statement is **true**.

2. **Statement II: A zero-order reaction is an elementary reaction.**
- A zero-order reaction means that the rate of reaction is independent of the concentration of the reactants. However, zero-order reactions can occur in complex mechanisms and are not necessarily elementary. An elementary reaction is defined as a reaction that occurs in a single step. Therefore, a zero-order reaction does not have to be elementary.
- **Conclusion:** This statement is **false**.

3. **Statement III: For elementary reactions, molecularity and order are equal.**
- By definition, molecularity refers to the number of reactant molecules involved in an elementary reaction, while the order of a reaction is the sum of the powers of the concentration terms in the rate law. For elementary reactions, these two values are indeed equal because the rate law can be directly derived from the stoichiometry of the reaction.
- **Conclusion:** This statement is **true**.

4. **Statement IV: Average and instantaneous rate of reaction are defined for micro and macroscopic time intervals respectively.**
- The average rate of reaction is calculated over a time interval (Δt) and gives an overall change in concentration over that period. In contrast, the instantaneous rate is defined at a specific moment in time (dt), not a macroscopic time interval. Thus, the terms "micro" and "macroscopic" do not accurately describe the time intervals for average and instantaneous rates.
- **Conclusion:** This statement is **false**.

### Final Evaluation:
- The correct statements are **I** and **III**.

### Summary of Correct Statements:
- **I) True**
- **II) False**
- **III) True**
- **IV) False**