Name the compound used to determine the hardness of water.

Explanation

To answer the question regarding the compound used to determine the hardness of water, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Water Hardness**:
- Water hardness is primarily due to the presence of certain minerals, especially calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These ions can interfere with the ability of soap to lather, which is a characteristic of hard water.

2. **Identifying the Compound**:
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