The experimental curve obtained when the rate of a reaction is plotted against the concentration of the reactant, appeared parallel to the concentration axis after sometime in a reaction. This indicates that

Options

A. the reaction is stopped
B. equilibrium is established
C. concentration of the reactant is negligible
D. the reaction is reomplex

Answer

To solve the question, we need to analyze the information provided about the experimental curve when the rate of a reaction is plotted against the concentration of the reactant.

### Step-by-Step Solution:

1. **Understanding the Graph**: The question states that the experimental curve of the reaction rate plotted against the concentration of the reactant becomes parallel to the concentration axis after some time. This implies that the rate of reaction does not change with further changes in the concentration of the reactant.

2. **Interpreting Parallelism**: When the graph becomes parallel to the concentration axis, it indicates that the rate of reaction has reached a constant value. This means that the reaction is no longer proceeding at a rate that depends on the concentration of the reactant.

3. **Reaction Dynamics**: Initially, as the reaction progresses, the concentration of the reactant decreases while the product concentration increases. However, once the graph becomes parallel to the concentration axis, it suggests that the rate of formation of products is equal to the rate of consumption of reactants.

4. **Establishment of Equilibrium**: The scenario described is characteristic of a chemical equilibrium. At equilibrium, the forward and reverse reactions occur at the same rate, leading to constant concentrations of both reactants and products.

5. **Conclusion**: Therefore, the observation that the graph becomes parallel to the concentration axis indicates that the equilibrium has been established in the reaction.

### Final Answer:
The experimental curve becoming parallel to the concentration axis indicates that **equilibrium is established** in the reaction.

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