Name the sodium compound which is used for softening hard water.

Explanation

**Step-by-Step Solution:**

1. **Understanding Hard Water**: Hard water is water that contains high concentrations of dissolved minerals, primarily calcium and magnesium ions. This makes it difficult for soap to lather.

2. **Identifying the Need for Softening**: To make hard water suitable for washing and other uses, it needs to be softened. Soft water allows soap to lather effectively and is better for cleaning purposes.

3. **Sodium Compound for Softening**: One of the common sodium compounds used for softening hard water is washing soda.

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