The time required for 100 percent completion of a zero order reaction is:

Options

A. `(2k)/a`
B. `a/(2k)`
C. `a/k`
D. `ak`

Explanation

To determine the time required for 100% completion of a zero-order reaction, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Zero-Order Reaction Kinetics**:
The rate of a zero-order reaction is constant and does not depend on the concentration of the reactants. The rate law can be expressed as:
\[ \text{Rate} = k \]
where \( k \) is the rate constant.

2. **Use the Integrated Rate Equation**:
For a zero-order reaction, the integrated rate equation is given by:
\[ [A] = [A_0] - kt \]
where:
- \([A]\) is the concentration of the reactant at time \( t \),
- \([A_0]\) is the initial concentration of the reactant,
- \( k \) is the rate constant,
- \( t \) is the time.

3. **Set Up the Equation for 100% Completion**:
At 100% completion, all of the reactant has been converted into products. Therefore, the concentration of the reactant \([A]\) becomes 0. Thus, we can set up the equation:
\[ 0 = [A_0] - kt \]

4. **Rearranging the Equation**:
Rearranging the equation to solve for \( t \):
\[ kt = [A_0] \]
\[ t = \frac{[A_0]}{k} \]

5. **Substituting Initial Concentration**:
Let’s denote the initial concentration of the reactant as \( A \) (i.e., \([A_0] = A\)):
\[ t = \frac{A}{k} \]

6. **Conclusion**:
Therefore, the time required for 100% completion of a zero-order reaction is:
\[ t = \frac{A}{k} \]

### Final Answer:
The time required for 100% completion of a zero-order reaction is \( \frac{A}{k} \).