The rate of reaction `A + B rarr` Product is given by the equation `r = k[A][B]`. If `B` is taken in large excess, the order of the reaction would be

Options

A. `a. 2`
B. `b. 1`
C. `c. 0`
D. d. Unpredictable

Explanation

To determine the order of the reaction when reactant B is taken in large excess, we can follow these steps:

### Step 1: Understand the Rate Equation
The given rate equation for the reaction \( A + B \rightarrow \text{Product} \) is:
\[ r = k[A][B] \]
where \( r \) is the rate of the reaction, \( k \) is the rate constant, and \([A]\) and \([B]\) are the concentrations of reactants A and B, respectively.

### Step 2: Consider B in Large Excess
When reactant B is taken in large excess, its concentration remains relatively constant throughout the reaction. This means that the change in concentration of B is negligible compared to A.

### Step 3: Simplify the Rate Expression
Since \([B]\) is constant, we can denote it as a new constant \( [B]_0 \). Thus, the rate expression can be rewritten as:
\[ r = k[A][B] \approx k[A][B]_0 \]
Here, \( k[B]_0 \) can be treated as a new effective rate constant \( k' \):
\[ r = k'[A] \]
where \( k' = k[B]_0 \).

### Step 4: Determine the Order of the Reaction
In this new rate expression \( r = k'[A] \), the rate of the reaction depends only on the concentration of A. The order of the reaction with respect to A is 1, since the rate is directly proportional to the concentration of A.

### Conclusion
Therefore, when B is taken in large excess, the order of the reaction is 1.

### Final Answer
The order of the reaction is 1.

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