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

Options

A. `A hArr B(K=10^3)`
B. `P hArr Q (K=10^(-2))`
C. `A +B hArr C+D (K=10)`
D. `X+Y hArr XY_2 (K=10^(-1))`

Answer

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

### Step-by-Step Solution:

1. **Understand the Concept of Equilibrium Constant (Kc)**:
- The equilibrium constant (Kc) is defined for a general reaction:
\[ aA + bB \rightleftharpoons cC + dD \]
as:
\[ K_c = \frac{[C]^c [D]^d}{[A]^a [B]^b} \]
- Here, \([C]\) and \([D]\) are the concentrations of the products, and \([A]\) and \([B]\) are the concentrations of the reactants.

2. **Analyze the Relationship Between Kc and Reaction Completion**:
- A higher value of Kc indicates a greater concentration of products at equilibrium. Therefore, if Kc is significantly greater than 1, it suggests that the reaction favors products, meaning it goes almost to completion.

3. **Evaluate the Given Options**:
- Suppose the options provided are:
- Option 1: Kc = \(10^3\)
- Option 2: Kc = \(10^1\)
- Option 3: Kc = \(10^{-1}\)
- Option 4: Kc = \(10^{-3}\)

4. **Compare the Values of Kc**:
- Among the given options, \(Kc = 10^3\) (Option 1) is the highest value.
- The other values \(10^1\), \(10^{-1}\), and \(10^{-3}\) are significantly lower than \(10^3\).

5. **Conclusion**:
- Since Option 1 has the highest Kc value, it indicates that the concentration of products is the highest in this reaction compared to the others.
- Therefore, the reaction corresponding to Option 1 goes almost to completion.

### Final Answer:
- The reaction that goes almost to completion is **Option 1: Kc = \(10^3\)**.