Which of the following ions will cause hardness in water ?

Explanation

To determine which ions cause hardness in water, we need to understand the types of hardness and the ions responsible for it.

### Step-by-Step Solution:

1. **Define Water Hardness**: Water hardness is primarily caused by the presence of certain dissolved minerals, mainly calcium (Ca²⁺) and magnesium (Mg²⁺) ions. Hard water can lead to scale buildup in pipes and appliances.

2. **Identify Common Hardness Ions**: The ions that typically contribute to water hardness include:
- Calcium ions (Ca²⁺)
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