A reaction proceeds in three stages, The first stage is a slow second order reaction, the second stage is fast and of first order, the third stage is fast and is a third order reaction. The overall order of the reaction is :

Options

A. First order
B. Second order
C. Third order
D. Zero order

Answer

To determine the overall order of the reaction that proceeds in three stages, we will analyze each stage and identify the rate-determining step (RDS). The overall order of a reaction is determined by the slowest step, which is the rate-determining step.

### Step-by-Step Solution:

1. **Identify the Stages of the Reaction**:
- The reaction proceeds in three stages:
- **First Stage**: A to B (slow, second order)
- **Second Stage**: B to C (fast, first order)
- **Third Stage**: C to E (fast, third order)

2. **Determine the Order of Each Stage**:
- The first stage is a second-order reaction. Therefore, its order is **2**.
- The second stage is a first-order reaction. Therefore, its order is **1**.
- The third stage is a third-order reaction. Therefore, its order is **3**.

3. **Identify the Rate-Determining Step (RDS)**:
- The first stage is specified as the slow step. Since the rate of the overall reaction is determined by the slowest step, the first stage (A to B) is the RDS.

4. **Determine the Overall Order of the Reaction**:
- The overall order of the reaction is equal to the order of the rate-determining step. Since the first stage is second order, the overall order of the reaction is **2**.

### Conclusion:
The overall order of the reaction is **2**.

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