Which is not present in clear hard water

Options

A. `Mg(HCO_(3))_(2)`
B. `CaCl_(2)`
C. `MgSO_(4)`
D. `MgCO_(3)`

Answer

To determine which substance is not present in clear hard water, we can analyze the components of hard water and its types.

### Step-by-Step Solution:

1. **Understanding Hard Water**:
Hard water is water that contains a high concentration of dissolved minerals, primarily calcium and magnesium ions.

2. **Types of Hard Water**:
There are two types of hard water:
- **Temporary Hard Water**: This type is primarily due to the presence of bicarbonates of calcium and magnesium (Ca(HCO3)2 and Mg(HCO3)2). It can be removed by boiling, which precipitates calcium carbonate (CaCO3) and magnesium carbonate (MgCO3).
- **Permanent Hard Water**: This type contains soluble salts such as chlorides and sulfates of calcium and magnesium (e.g., CaCl2, MgSO4).

3. **Components of Hard Water**:
- Temporary hardness involves bicarbonates, which can be converted to insoluble carbonates upon boiling.
- Permanent hardness involves chlorides and sulfates, which remain in solution even after boiling.

4. **Identifying the Substance Not Present**:
Since the question asks for a substance not present in clear hard water, we need to consider the components that are typically found in hard water.
- Bicarbonates, chlorides, and sulfates are present in hard water.
- However, substances like magnesium carbonate (MgCO3) are formed as a result of the decomposition of magnesium bicarbonate when boiled and are not present in the original hard water.

5. **Conclusion**:
Therefore, the substance that is not present in clear hard water is **magnesium carbonate (MgCO3)**, as it is formed after the decomposition of magnesium bicarbonate and is not found in the original hard water.

### Final Answer:
**Magnesium Carbonate (MgCO3)** is not present in clear hard water.

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