Which of the following is most effective in coagulating positively charged methylene blue sol?

Options

A. `Na_3PO_4`
B. `K_[Fe(CN)_6]`
C. `Na_2SO_4`
D. `Al_2(SO_4)_3`

Explanation

To determine which substance is most effective in coagulating positively charged methylene blue sol, we need to follow these steps:

### Step 1: Understand the Charge of Methylene Blue
Methylene blue is a cationic dye, meaning it carries a positive charge. To coagulate this positively charged sol, we need to introduce a substance that carries a negative charge.

### Step 2: Identify the Options
We need to look at the options provided to find substances that have a negative charge. The options given are:
1. PO4^3-
2. K4[Fe(CN)6]
3. SO4^2-
4. (Assuming there is a fourth option, but it is not provided)

### Step 3: Determine the Charge of Each Option
- **PO4^3-**: This ion has a charge of -3.
- **K4[Fe(CN)6]**: This compound contains the [Fe(CN)6]4- ion, which has a charge of -4.
- **SO4^2-**: This ion has a charge of -2.

### Step 4: Compare the Negative Charges
Now, we compare the negative charges of the identified options:
- PO4^3- has a charge of -3.
- K4[Fe(CN)6] has a charge of -4.
- SO4^2- has a charge of -2.

### Step 5: Conclusion
Since we need the most effective coagulating agent, we should choose the one with the highest negative charge. Among the options, K4[Fe(CN)6] has the most negative charge (-4), making it the most effective in coagulating positively charged methylene blue sol.

### Final Answer
The most effective substance in coagulating positively charged methylene blue sol is **K4[Fe(CN)6]**.

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