Which of the following is pseudo-unimolecular reaction ?

Options

A. `2H_2O_2rarr2H_2O+O_2`
B. `C_6H_5N_2Cl+HOHrarrC_6H_5OH+N_2+HCl`
C. `CH_3COOC_2H_5+NaOHrarrCH_3COONa+C_2H_5OH`
D. `2O_3+3O_2`

Answer

To determine which of the following is a pseudo-unimolecular reaction, we first need to understand what a pseudo-unimolecular reaction is.

### Step-by-Step Solution:

1. **Definition of Pseudo-Unimolecular Reaction**:
A pseudo-unimolecular reaction is a reaction that appears to be first-order because one of the reactants is present in a large excess. This excess reactant's concentration remains relatively constant during the reaction, allowing us to simplify the rate law.

2. **Identify Hydrolysis Reactions**:
Hydrolysis reactions are common examples of pseudo-unimolecular reactions. In these reactions, water is typically the reactant that is present in a large excess.

3. **Analyze the Given Options**:
We need to look at the options provided and identify which one represents a hydrolysis reaction. The question states that hydrolysis reactions are pseudo-unimolecular because the concentration of water remains constant due to its excess.

4. **Select the Correct Option**:
Among the options, we find that only option number 2 depicts a hydrolysis reaction. In this case, water acts as a reactant, and since it is in excess, its concentration does not significantly change during the reaction.

5. **Rate Law Consideration**:
For the reaction in option 2, the rate of the reaction depends on the concentration of C6H5N2Cl and the concentration of water. However, since water is in excess, we can treat its concentration as constant. Thus, the rate law can be simplified to:
\[ \text{Rate} = k' [C6H5N2Cl] \]
where \( k' = k \times [H2O] \) (a constant). This simplification shows that the reaction behaves as a first-order reaction with respect to C6H5N2Cl.

6. **Conclusion**:
Therefore, the correct answer to the question is option number 2, which represents a pseudo-unimolecular reaction.