A reaction is 50 % complete in 2 hours and 75 % complete in 4 hours the order of reaction is

Options

A. 0
B. 1
C. 2
D. 3

Answer

To determine the order of the reaction based on the given information, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Given Data**:
- The reaction is 50% complete in 2 hours.
- The reaction is 75% complete in 4 hours.

2. **Identifying Concentrations**:
- Let the initial concentration of the reactant be \( A \).
- After 2 hours, the concentration becomes \( \frac{A}{2} \) (50% completion).
- After 4 hours, the concentration becomes \( \frac{A}{4} \) (75% completion).

3. **Calculating Half-Life**:
- The time taken to go from \( A \) to \( \frac{A}{2} \) is 2 hours.
- The time taken to go from \( \frac{A}{2} \) to \( \frac{A}{4} \) is also 2 hours.
- This indicates that the half-life of the reaction is constant and equals 2 hours.

4. **Relating Half-Life to Reaction Order**:
- For a first-order reaction, the half-life is constant and does not depend on the concentration of the reactant.
- Since we have observed that the half-life remains constant (2 hours) for both intervals, we can conclude that the reaction follows first-order kinetics.

5. **Conclusion**:
- Therefore, the order of the reaction is **first order**.