A reaction is `50%` complete in 2 hours and `75%` complete in 4 hours. What is the order of reaction?

Options

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

Answer

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

### Step 1: Understand the Given Data
We know that:
- The reaction is 50% complete in 2 hours.
- The reaction is 75% complete in 4 hours.

### Step 2: Analyze the Half-Life
For a reaction to be classified as first order, the half-life (T1/2) should remain constant regardless of the concentration of the reactant.

From the data:
- At 2 hours, the concentration of the reactant has decreased to 50% of its initial value.
- At 4 hours, the concentration of the reactant has decreased to 25% of its initial value (since 75% is complete).

### Step 3: Calculate the Time Intervals
The time taken to go from 50% to 75% completion is 2 hours (from 2 hours to 4 hours).

### Step 4: Determine the Nature of the Reaction
In a first-order reaction:
- The half-life is constant.
- The same time interval (2 hours) is taken to go from 50% to 75% completion, which indicates that the time required to reduce the concentration by half remains the same.

### Step 5: Conclusion
Since the time taken to go from 50% to 75% completion is the same as the time taken to go from 0% to 50% completion, this behavior is characteristic of a first-order reaction.

Thus, we can conclude that the order of the reaction is **first order**.

### Final Answer
The order of the reaction is **first order**.

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