In which of the following does the reaction go almost to completion?

Options

A. `A+BhArrC," "K=10^(4)`
B. `X+YhArrZ," "K=10^(-3)`
C. `P+QhArrR," "K=1`
D. `M+NhArrO+P,K=10^(-1)`

Answer

To determine in which of the following reactions the reaction goes almost to completion, we need to analyze the given equilibrium constants (K) for each reaction. The higher the value of K, the more the reaction favors the formation of products, indicating that the reaction goes closer to completion.

### Step-by-Step Solution:

1. **Understand the Concept of Equilibrium Constant (K)**:
The equilibrium constant (K) is defined as:
\[ K = \frac{[\text{Products}]}{[\text{Reactants}]} \]
A larger value of K indicates that at equilibrium, the concentration of products is much greater than that of reactants.

2. **Analyze Each Reaction**:
- **Reaction 1**: \( A + B \rightleftharpoons C \), \( K = 10^4 \)
- **Reaction 2**: \( X + Y \rightleftharpoons Z \), \( K = 10^{-3} \)
- **Reaction 3**: \( P + Q \rightleftharpoons R \), \( K = 1 \)
- **Reaction 4**: \( M + N \rightleftharpoons O + P \), \( K = 10^{-1} \)

3. **Compare the Values of K**:
- For Reaction 1, \( K = 10^4 \) (very large, favors products)
- For Reaction 2, \( K = 10^{-3} \) (very small, favors reactants)
- For Reaction 3, \( K = 1 \) (balanced)
- For Reaction 4, \( K = 10^{-1} \) (favors reactants)

4. **Determine Which Reaction Goes to Completion**:
The reaction that goes almost to completion will have the largest K value. In this case, Reaction 1 with \( K = 10^4 \) has the highest value among the options provided.

5. **Conclusion**:
Therefore, the reaction that goes almost to completion is:
\[ \text{Answer: Reaction 1 ( } A + B \rightleftharpoons C, K = 10^4 \text{ )} \]