Which statement is correct ?

Options

A. Molecularity of a reaction is same as the order of reaction
B. In some cases order of reaction may be same as the molecularity of the reaction
C. Molecularity may be zero
D. Molecularity may be fractional

Answer

To determine which statement is correct regarding the relationship between molecularity and order of a reaction, we need to analyze the definitions and characteristics of both concepts.

### Step-by-Step Solution:

1. **Understanding Molecularity**:
- Molecularity refers to the number of reactant molecules that collide in an elementary reaction step. It is a theoretical concept and is always a whole number (1, 2, 3, etc.). It cannot be zero, negative, or fractional.

2. **Understanding Order of Reaction**:
- The order of a reaction is determined experimentally and refers to the power to which the concentration of a reactant is raised in the rate law expression. The order can be zero, positive, negative, or fractional.

3. **Comparison of Molecularity and Order**:
- In some cases, the order of a reaction may be the same as its molecularity. For example, in a simple elementary reaction where two molecules collide, both the order and molecularity would be 2.
- However, there are many instances where the order does not equal the molecularity. For example, in a reaction where the rate depends on the concentration of one reactant raised to a power, the order can be different from the molecularity.

4. **Examples**:
- Consider the reaction:
\[ R-C(O)-O-R + H_2O \rightarrow R-OH + R-COOH \]
Here, the molecularity is 2 (two molecules are involved), but the order may be 1 based on experimental data.
- Another example is the decomposition of \(N_2O_5\):
\[ 2N_2O_5 \rightarrow 4N_2O_4 + O_2 \]
In this case, both the order and molecularity can be 1.

5. **Conclusion**:
- Therefore, the statement "the molecularity of a reaction is the same as the order of the reaction" is not universally true. It can be true in some specific cases, but not in general. Hence, the statement is incorrect.

### Final Answer:
The correct statement is: "In some cases, the order and molecularity of a reaction can be the same."