In which of the following reactions, the concentration of rectant is equal to concentration of product at equilibrium (K=equilibrium constant)

Options

A. `A Leftrightarrow B, K=0.01`
B. `R Leftrightarrow P, K=1`
C. `X Leftrightarrow Y, K=10`
D. `L Leftrightarrow J, K=0.025`

Answer

To determine in which of the following reactions the concentration of reactants is equal to the concentration of products at equilibrium, we will analyze each reaction based on the equilibrium constant (K) provided.

### Step-by-Step Solution:

1. **Understanding Equilibrium Constant (K)**:
The equilibrium constant (K) for a reaction at equilibrium is defined as the ratio of the concentration of products to the concentration of reactants. If K = 1, it indicates that the concentrations of reactants and products are equal.

2. **Analyzing Each Reaction**:
We will evaluate each given reaction based on its equilibrium constant.

**Reaction A**:
\[ A \rightleftharpoons B \]
Given \( K = 0.01 \)
- The expression for K is:
\[ K = \frac{[B]}{[A]} = 0.01 \]
- Rearranging gives:
\[ [B] = 0.01 \times [A] \]
- Here, the concentration of product (B) is much less than that of reactant (A). Thus, they are not equal.

**Reaction B**:
\[ R \rightleftharpoons P \]
Given \( K = 1 \)
- The expression for K is:
\[ K = \frac{[P]}{[R]} = 1 \]
- Rearranging gives:
\[ [P] = [R] \]
- Here, the concentrations of reactant (R) and product (P) are equal. This reaction satisfies the condition.

**Reaction C**:
\[ X \rightleftharpoons Y \]
Given \( K = 10 \)
- The expression for K is:
\[ K = \frac{[Y]}{[X]} = 10 \]
- Rearranging gives:
\[ [Y] = 10 \times [X] \]
- Here, the concentration of product (Y) is much greater than that of reactant (X). Thus, they are not equal.

**Reaction D**:
\[ L \rightleftharpoons J \]
Given \( K = 0.025 \)
- The expression for K is:
\[ K = \frac{[J]}{[L]} = 0.025 \]
- Rearranging gives:
\[ [J] = 0.025 \times [L] \]
- Here, the concentration of product (J) is much less than that of reactant (L). Thus, they are not equal.

3. **Conclusion**:
After analyzing all four reactions, we find that only in **Reaction B** is the concentration of reactants equal to the concentration of products at equilibrium.

### Final Answer:
The correct option is **Reaction B** where the concentration of reactant is equal to the concentration of product at equilibrium.