Reaction :`2Br^- +H_2O_2+2H^+ to Br_2+2H_2O` takes place in two steps:
(a) `Br^- +H_2O_2 +H^+ to^(slow) HOBr+H_2O`
(b) `HOBr+Br^- +H^+ to^(fast) H_2O+Br_2`
The order of the reaction is

Options

A. 3
B. 6
C. 5
D. 0

Answer

To determine the order of the reaction given by the steps:

1. **Identify the rate-determining step**: The first step of the reaction is labeled as slow, which indicates that it is the rate-determining step. This means that the rate of the overall reaction is governed by this step.

2. **Write the rate law for the rate-determining step**: The first step is:
\[ \text{Br}^- + \text{H}_2\text{O}_2 + \text{H}^+ \rightarrow \text{HOBr} + \text{H}_2\text{O} \]
The rate law can be expressed as:
\[ \text{Rate} = k[\text{Br}^-][\text{H}_2\text{O}_2][\text{H}^+] \]
Here, \(k\) is the rate constant, and the concentrations of the reactants are included.

3. **Determine the order of the reaction**: The order of the reaction is determined by the sum of the powers of the concentration terms in the rate law. In this case:
- The power of \([\text{Br}^-]\) is 1.
- The power of \([\text{H}_2\text{O}_2]\) is 1.
- The power of \([\text{H}^+]\) is 1.

Therefore, the overall order of the reaction is:
\[ 1 + 1 + 1 = 3 \]

4. **Conclude the order of the reaction**: The order of the reaction is 3, which indicates that it is a third-order reaction.

### Final Answer:
The order of the reaction is **3**.

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