Which of the following pair of ions makes the water hard(temporary) ?

Explanation

To determine which pair of ions makes water temporarily hard, we need to understand the characteristics of temporary hardness in water.

### Step-by-Step Solution:

1. **Understanding Water Hardness**:
- Water hardness is classified into two types: temporary hardness and permanent hardness.
- Temporary hardness is primarily due to the presence of bicarbonate (HCO3-) and carbonate (CO3^2-) ions of calcium (Ca^2+) and magnesium (Mg^2+).

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