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 given options the reaction goes almost to completion, we need to analyze the equilibrium constant (K) values provided for each option. The larger the value of K, the more the reaction favors the products, indicating that the reaction goes almost to completion.

### Step-by-Step Solution:

1. **Understand the Concept of Equilibrium Constant (K)**:
- The equilibrium constant (K) is a measure of the ratio of the concentration of products to the concentration of reactants at equilibrium.
- A large K value (much greater than 1) indicates that the products are favored, meaning the reaction goes almost to completion.

2. **Analyze Each Option**:
- **Option A**: K = 10^4
- **Option B**: K = 10^-3
- **Option C**: K = k1 (not specified, but we will assume it is a small value)
- **Option D**: K = 10^-1

3. **Compare the K Values**:
- **Option A (K = 10^4)**: This is a large value, indicating that the reaction goes almost to completion.
- **Option B (K = 10^-3)**: This is a small value, indicating that the reaction does not proceed significantly towards products.
- **Option C (K = k1)**: Without a specific value, we cannot determine its effect, but if it is less than 1, it would not favor products.
- **Option D (K = 10^-1)**: This is also a small value, indicating that the reaction does not proceed significantly towards products.

4. **Conclusion**:
- The only option where the reaction goes almost to completion is **Option A (K = 10^4)**.

### Final Answer:
The reaction goes almost to completion in **Option A (K = 10^4)**.