When initial concentration of a reactant is doubled in a reaction, its half-life period is not affected. The order of the reaction is

Options

A. More than zero but less than first
B. Zero
C. First
D. Second

Answer

To determine the order of the reaction based on the information that doubling the initial concentration of a reactant does not affect its half-life period, we can analyze the relationship between half-life and concentration for different orders of reactions.

### Step-by-Step Solution:

1. **Understanding Half-Life**:
The half-life (T½) of a reaction is the time required for the concentration of a reactant to decrease to half of its initial value.

2. **Analyzing the Effect of Concentration on Half-Life**:
- For different orders of reactions, the half-life depends on the concentration of the reactant in different ways:
- **Zero Order Reaction**:
\[ T_{1/2} \propto [A] \]
Here, if the concentration of A is doubled, T½ will also double.
- **First Order Reaction**:
\[ T_{1/2} = \frac{0.693}{k} \]
In this case, T½ is independent of the concentration of A. Doubling the concentration does not affect the half-life.
- **Second Order Reaction**:
\[ T_{1/2} \propto \frac{1}{[A]} \]
Here, if the concentration of A is doubled, T½ will be halved.

3. **Conclusion from the Given Information**:
Since the problem states that doubling the concentration does not affect the half-life, we can conclude that the reaction cannot be zero or second order because in those cases, the half-life would change with concentration.

4. **Final Determination**:
The only order of reaction where the half-life remains constant regardless of concentration is the **first order** reaction.

Thus, the order of the reaction is **first order**.