Name the compound used for measuring the hardness of water, i.e., for estimation of `Ca^(2+)` and `Mg^(2+)` ions.

Explanation

To solve the question, we need to identify the compound used for measuring the hardness of water, specifically for estimating the concentrations of calcium ions (Ca²⁺) and magnesium ions (Mg²⁺) in water.

### Step-by-Step Solution:

1. **Understanding Water Hardness**:
- Water hardness is primarily due to the presence of dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These ions can come from natural sources or can be introduced through human activities.

2. **Identifying the Measurement Method**:
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