For the complex `ML_(2) ` stepwise formation constants for
`M+L hArr ML `
`ML+L hArr ML_(2)`
are 4 and 3 . Hence overcell stability constant for ` M +2L hArr ML_(2)` is

Options

A. 12
B. 7
C. 1.33
D. 0.75

Answer

To find the overall stability constant (cumulative constant) for the complex formation reaction \( M + 2L \rightleftharpoons ML_2 \), we will use the stepwise formation constants provided.

### Step-by-Step Solution:

1. **Identify the Stepwise Formation Constants**:
- The first step is the formation of \( ML \) from \( M \) and \( L \):
\[ M + L \rightleftharpoons ML \]
The formation constant for this reaction is given as \( K_1 = 4 \).

- The second step is the formation of \( ML_2 \) from \( ML \) and \( L \):
\[ ML + L \rightleftharpoons ML_2 \]
The formation constant for this reaction is given as \( K_2 = 3 \).

2. **Write the Expression for the Overall Stability Constant**:
- The overall stability constant \( \beta_{1,2} \) for the reaction \( M + 2L \rightleftharpoons ML_2 \) can be expressed as the product of the stepwise constants:
\[ \beta_{1,2} = K_1 \times K_2 \]

3. **Substitute the Values of \( K_1 \) and \( K_2 \)**:
- Substitute the values we have:
\[ \beta_{1,2} = 4 \times 3 \]

4. **Calculate the Overall Stability Constant**:
- Perform the multiplication:
\[ \beta_{1,2} = 12 \]

5. **Conclusion**:
- The overall stability constant for the reaction \( M + 2L \rightleftharpoons ML_2 \) is:
\[ \beta_{1,2} = 12 \]

### Final Answer:
The overall stability constant for \( M + 2L \rightleftharpoons ML_2 \) is **12**.