Rate constant of two reactions are given below. Indentifying their order of reaction.
(i) `k = 6.3 xx 10^(-2) L mol^(-1) s^(-1)`
(ii) `k = 2.8 xx 10^(-4) s^(-1)`

Options

A. (i) second order, (ii) first order
B. (i) first order, (ii) second order
C. (i) zero order, (ii) first order
D. (i) second order, (ii) zero order

Answer

To determine the order of the reactions based on the given rate constants, we can analyze the units of the rate constants provided.

### Step-by-Step Solution:

1. **Identify the Units of the Rate Constants:**
- For the first reaction, the rate constant \( k = 6.3 \times 10^{-2} \, \text{L mol}^{-1} \text{s}^{-1} \).
- For the second reaction, the rate constant \( k = 2.8 \times 10^{-4} \, \text{s}^{-1} \).

2. **Use the General Formula for Rate Constants:**
The general formula for the rate constant \( k \) is given by:
\[ k = \text{(concentration)}^{(1-n)} \cdot \text{(time)}^{-1} \]
where \( n \) is the order of the reaction.

3. **Determine the Order of the First Reaction:**
- For the first reaction, we have:
\[ k = 6.3 \times 10^{-2} \, \text{L mol}^{-1} \text{s}^{-1} \]
- The units can be compared to the general formula:
\[ 1 - n = -1 \quad \text{(since we have L mol}^{-1} \text{s}^{-1}\text{)} \]
- Rearranging gives:
\[ n = 2 \]
- Therefore, the first reaction is a **second-order reaction**.

4. **Determine the Order of the Second Reaction:**
- For the second reaction, we have:
\[ k = 2.8 \times 10^{-4} \, \text{s}^{-1} \]
- The units here suggest:
\[ 1 - n = 0 \quad \text{(since there are no units of concentration)} \]
- Rearranging gives:
\[ n = 1 \]
- Therefore, the second reaction is a **first-order reaction**.

5. **Conclusion:**
- The order of the first reaction is **second-order**.
- The order of the second reaction is **first-order**.

### Final Answer:
- First reaction: Second-order
- Second reaction: First-order