Which of the following curves represents a zero order reaction ? [`(a-x)` =reactant concn.]

Options

A.
B.
C.
D.

Answer

To determine which curve represents a zero-order reaction, we need to understand the characteristics of zero-order kinetics and how they are represented graphically.

### Step-by-Step Solution:

1. **Understand Zero-Order Reactions**:
- In a zero-order reaction, the rate of reaction is constant and does not depend on the concentration of the reactant. This means that the rate of reaction remains the same regardless of how much reactant is present.

2. **Rate Law for Zero-Order Reactions**:
- The rate law for a zero-order reaction can be expressed as:
\[ \text{Rate} = k \]
- Here, \( k \) is the rate constant.

3. **Integrated Rate Equation**:
- The integrated rate equation for a zero-order reaction 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.

4. **Graphical Representation**:
- When we plot the concentration of the reactant \([A]\) (or \(A - x\), where \(x\) is the amount of reactant that has reacted) against time \(t\), we get a straight line.
- The slope of this line is negative and equal to \(-k\).
- The y-intercept of this graph is the initial concentration \([A_0]\).

5. **Identifying the Correct Curve**:
- To identify which curve represents a zero-order reaction, look for a straight line with a negative slope when plotting \([A]\) (or \(A - x\)) on the y-axis and time \(t\) on the x-axis.
- If the graph is linear and decreases over time, it indicates a zero-order reaction.

### Conclusion:
Based on the characteristics and graphical representation of zero-order reactions, the correct curve will be the one that shows a straight line with a negative slope when plotting the concentration of the reactant against time.