Salt of the following is used as a water softner

Options

A. `H_(4)P_(2)O_(6)`
B. `H_(4)P_(2)O_(7)`
C. `HPO_(3)`
D. `HPO_(2)`

Answer

To determine which salt is used as a water softener from the given options (H4P2O6, H4P2O7, HPO3, and HPO2), we can follow these steps:

### Step 1: Understand what a water softener is
Water softeners are substances that remove hardness from water, which is typically caused by the presence of calcium and magnesium ions. They often work by replacing these ions with sodium ions.

### Step 2: Identify the salts related to the given acids
The question provides four different phosphoric acids:
- H4P2O6 (Pyrophosphoric acid)
- H4P2O7 (Diphosphoric acid)
- HPO3 (Meta-phosphoric acid)
- HPO2 (Hypophosphorous acid)

### Step 3: Research common water softeners
One of the most common water softeners is sodium hexametaphosphate, which is represented by the formula Na6P6O18. This compound is derived from meta-phosphoric acid (HPO3).

### Step 4: Determine the correct option
Since sodium hexametaphosphate is a salt of meta-phosphoric acid (HPO3), we can conclude that the correct answer to the question is HPO3.

### Final Answer
The salt of HPO3 (meta-phosphoric acid) is used as a water softener.

---