The rate constant of a reaction has same units as the rate of reaction. The reaction is of:

Options

A. zero order
B. first order
C. second order
D. none of these

Explanation

To solve the problem, we need to determine the order of the reaction based on the relationship between the rate constant (k) and the rate of reaction (R). The key point is that the units of k must be the same as the units of R.

### Step-by-Step Solution:

1. **Understanding Rate of Reaction**:
The rate of a reaction (R) is defined as the change in concentration of a reactant or product per unit time. The units for rate are typically expressed as:
\[ \text{Rate (R)} = \frac{\text{moles}}{\text{liter} \cdot \text{second}} = \text{mol L}^{-1} \text{s}^{-1} \]

2. **Rate Law Expression**:
The rate law for a reaction can be expressed as:
\[ R = k [A]^n \]
where:
- \( R \) is the rate of reaction,
- \( k \) is the rate constant,
- \([A]\) is the concentration of reactant A,
- \( n \) is the order of the reaction.

3. **Analyzing Units for Different Orders**:
- For **zero-order reactions** (\( n = 0 \)):
\[ R = k \]
Here, the rate constant \( k \) has the same units as the rate of reaction, which is \( \text{mol L}^{-1} \text{s}^{-1} \).

- For **first-order reactions** (\( n = 1 \)):
\[ R = k [A] \]
Rearranging gives:
\[ k = \frac{R}{[A]} \]
The units of \( k \) become:
\[ k = \frac{\text{mol L}^{-1} \text{s}^{-1}}{\text{mol L}^{-1}} = \text{s}^{-1} \]
Here, the units of \( k \) are not the same as the units of \( R \).

- For **second-order reactions** (\( n = 2 \)):
\[ R = k [A]^2 \]
Rearranging gives:
\[ k = \frac{R}{[A]^2} \]
The units of \( k \) become:
\[ k = \frac{\text{mol L}^{-1} \text{s}^{-1}}{(\text{mol L}^{-1})^2} = \text{L mol}^{-1} \text{s}^{-1} \]
Again, the units of \( k \) are not the same as the units of \( R \).

4. **Conclusion**:
The only case where the units of the rate constant \( k \) and the rate of reaction \( R \) are the same is for a zero-order reaction. Therefore, the order of the reaction is:
\[ \text{Order of the reaction} = 0 \]

### Final Answer:
The reaction is of **zero order**.