Arrange the following substances in order of increasing ability to coagulate i) negative change sol and ii) a positively change sol: `X) ZnSO_4, Y) AlCl_3` and `Z) Na_3PO_4`.

Answer

To solve the problem of arranging the substances in order of increasing ability to coagulate, we will analyze the given electrolytes based on the principles of coagulation, specifically using Schulze-Hardy rule.

### Step-by-Step Solution:

1. **Identify the Charges of the Colloids:**
- We have two types of sols: negatively charged sol and positively charged sol.
- For negatively charged sols, we need positively charged ions (cations) for coagulation.
- For positively charged sols, we need negatively charged ions (anions) for coagulation.

2. **List the Given Electrolytes:**
- X) ZnSO₄ (provides Zn²⁺ and SO₄²⁻)
- Y) AlCl₃ (provides Al³⁺ and Cl⁻)
- Z) Na₃PO₄ (provides Na⁺ and PO₄³⁻)

3. **Coagulation Ability for Positively Charged Sols:**
- For positively charged sols, we need to consider the negative ions (anions) from the electrolytes:
- SO₄²⁻ (from ZnSO₄) has a charge of -2.
- Cl⁻ (from AlCl₃) has a charge of -1.
- PO₄³⁻ (from Na₃PO₄) has a charge of -3.
- According to Schulze-Hardy rule, the coagulation power increases with the charge of the ion. Therefore, the order of coagulation ability for negatively charged ions is:
- Z (PO₄³⁻) > X (SO₄²⁻) > Y (Cl⁻)
- Thus, for positively charged sols, the order is:
- Z > X > Y

4. **Coagulation Ability for Negatively Charged Sols:**
- For negatively charged sols, we need to consider the positive ions (cations) from the electrolytes:
- Zn²⁺ (from ZnSO₄) has a charge of +2.
- Al³⁺ (from AlCl₃) has a charge of +3.
- Na⁺ (from Na₃PO₄) has a charge of +1.
- Again, according to Schulze-Hardy rule, the coagulation power increases with the charge of the ion. Therefore, the order of coagulation ability for positively charged ions is:
- Y (Al³⁺) > X (Zn²⁺) > Z (Na⁺)
- Thus, for negatively charged sols, the order is:
- Y > X > Z

5. **Final Arrangement:**
- For negatively charged sols: Y > X > Z
- For positively charged sols: Z > X > Y

### Summary of Orders:
- For negatively charged sols: **Y > X > Z**
- For positively charged sols: **Z > X > Y**