The reaction `L to ` M is started with 10 g of L .A After 30 and 90 minute , 5g and 1.25 g of L are left respectively . The order of reaction is

Options

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

Explanation

To determine the order of the reaction \( L \to M \) given the data, we can follow these steps:

### Step 1: Gather Initial Information
We start with 10 g of \( L \). After 30 minutes, 5 g of \( L \) remains, and after 90 minutes, 1.25 g of \( L \) remains.

### Step 2: Calculate the Amount of \( L \) Consumed
- After 30 minutes:
\[ \text{Amount consumed} = 10 \, \text{g} - 5 \, \text{g} = 5 \, \text{g} \]
- After 90 minutes:
\[ \text{Amount consumed} = 10 \, \text{g} - 1.25 \, \text{g} = 8.75 \, \text{g} \]

### Step 3: Determine the Time Intervals
- The time interval from the start to 30 minutes is 30 minutes.
- The time interval from 30 minutes to 90 minutes is 60 minutes.

### Step 4: Analyze the Change in Concentration
- From 10 g to 5 g in 30 minutes (50% remaining).
- From 10 g to 1.25 g in 90 minutes (12.5% remaining).

### Step 5: Calculate Half-Lives
- The half-life for the first interval (10 g to 5 g) is 30 minutes.
- The half-life for the second interval (5 g to 2.5 g) would also be 30 minutes if we continued this process, but we see that it is not directly measured here.

### Step 6: Determine Order of Reaction
- For a zero-order reaction, the half-life depends on the concentration. If we observe that the half-life changes with concentration, it would indicate a zero-order reaction.
- For a first-order reaction, the half-life is constant regardless of concentration. Since the time taken to reduce from 10 g to 5 g (30 minutes) and from 5 g to 1.25 g (60 minutes) shows a consistent pattern, we can conclude that the half-life remains the same (30 minutes).

### Conclusion
Since the half-life remains constant, we can conclude that the reaction is a **first-order reaction**.

### Final Answer
The order of the reaction \( L \to M \) is **first order**.

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