Which of the following statement is not correct about order of a reaction ?

Options

A. Order of a reaction can be determined experimentally
B. It is the sum of the powers of concentration terms in the rate law expression
C. It does not necessarily depend upon the stoichiometric coefficients
D. Order of a reaction cannot be fractional

Explanation

**Step-by-Step Solution:**

To determine which statement is not correct about the order of a reaction, we will analyze each option provided.

1. **Option 1: The order of a reaction can be determined experimentally.**
- This statement is **correct**. The order of a reaction is determined through experimental data and is not necessarily related to the stoichiometric coefficients of the reactants. For example, the decomposition of N2O5 can be shown to be a first-order reaction based on experimental results.

2. **Option 2: The order of a reaction is the sum of the powers of the concentration terms in the rate law expression.**
- This statement is also **correct**. The order of a reaction is indeed calculated by summing the powers of the concentration terms in the rate law expression. For example, if the rate law is expressed as \( r = k[A]^m[B]^n \), then the order of the reaction is \( m + n \).

3. **Option 3: The order of a reaction does not necessarily depend upon the stoichiometry coefficients.**
- This statement is **correct**. The order of a reaction can differ from the stoichiometric coefficients. For example, in a reaction where the stoichiometry is \( A + B \rightarrow C \), the rate law could be \( r = k[A]^2[B]^1 \), indicating that the order is 3, while the stoichiometric coefficients are 1 for A and 1 for B.

4. **Option 4: The order of a reaction is always a whole number.**
- This statement is **not correct**. The order of a reaction can be a fraction or even zero. For example, a reaction can have a fractional order if the rate law includes non-integer powers of concentration terms.

**Conclusion:**
The statement that is not correct about the order of a reaction is **Option 4: The order of a reaction is always a whole number.**

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