The best electrolyte for coagulating `As_(2)S_(3)` sol is

Options

A. `NaCl`
B. `CuSO_(4)`
C. `Al(NO_(3))_(3)`
D. `Th(SO_(4))_(2)`

Answer

To determine the best electrolyte for coagulating As₂S₃ sol, we can follow these steps:

### Step 1: Understand the nature of As₂S₃ sol
As₂S₃ (arsenic trisulfide) is a colloidal sol that carries a negative charge. The particles in this sol are stabilized by their negative charge, which prevents them from aggregating and precipitating.

**Hint:** Identify the charge of the colloidal particles to understand how they interact with electrolytes.

### Step 2: Define coagulation
Coagulation is the process where colloidal particles come together to form larger aggregates, leading to precipitation. For coagulation to occur, the repulsive forces between the negatively charged particles must be neutralized.

**Hint:** Coagulation involves neutralizing the charge of colloidal particles to allow them to aggregate.

### Step 3: Identify the role of electrolytes
Electrolytes are substances that dissociate into ions in solution. To coagulate a negatively charged sol like As₂S₃, we need to introduce a cation (positive ion) that can neutralize the negative charge of the sol particles.

**Hint:** Look for cations that can effectively neutralize the negative charge of the sol.

### Step 4: Apply Hardy's rule
According to Hardy's rule, the coagulating power of an electrolyte is proportional to the charge of its ions. Therefore, cations with higher positive charges will be more effective in coagulating the negatively charged As₂S₃ sol.

**Hint:** Compare the charges of different cations to determine which one has the highest charge.

### Step 5: Compare common cations
- Na⁺ (from NaCl) has a +1 charge.
- K⁺ (from KCl) has a +1 charge.
- Ca²⁺ (from CaCl₂) has a +2 charge.
- Al³⁺ (from AlCl₃) has a +3 charge.
- Th⁴⁺ (from ThCl₄) has a +4 charge.

Among these, Th⁴⁺ has the highest charge.

**Hint:** Identify the cation with the highest positive charge to determine the best electrolyte.

### Step 6: Conclusion
The best electrolyte for coagulating As₂S₃ sol is ThCl₄ (Thorium chloride), as Th⁴⁺ has the highest charge and will effectively neutralize the negative charge of the As₂S₃ particles, leading to coagulation.

**Final Answer:** The best electrolyte for coagulating As₂S₃ sol is ThCl₄.