Which chemical is used in softening of hard water by Clark's method?

Explanation

**Step-by-Step Solution:**

1. **Understanding Hard Water:**
- Hard water contains high concentrations of minerals, primarily calcium and magnesium salts. These minerals contribute to the hardness of the water, making it less suitable for certain uses, such as washing and cooking.

2. **Definition of Soft Water:**
- Soft water is defined as water that has a low concentration of ions, particularly calcium and magnesium. This type of water is more desirable for various applications because it does not form scale and allows soaps to lather more effectively.

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