Hardness of water is due to
(a)`Ca^(2+)` and `K^(+)`
(b)`Mg^(2+)` and `K^(+)`
(c)`Ca^(2+)` and `Mg^(2+)`
(d)`Ba^(2+)` and `Zn^(2+)`

Options

A. `Ca^(2+)` and `K^(+)`
B. `Mg^(2+)` and `K^(+)`
C. `Ca^(2+)` and `Mg^(2+)`
D. `Ba^(2+)` and `Zn^(2+)`

Answer

To determine the cause of water hardness, we need to analyze the options given in the question.

### Step-by-Step Solution:

1. **Understanding Water Hardness**:
- Water hardness is primarily caused by the presence of certain minerals in water, particularly calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These ions can come from various sources, including soluble bicarbonates, chlorides, and sulfates.

2. **Analyzing the Options**:
- (a) `Ca^(2+)` and `K^(+)`: Potassium (K⁺) does not contribute to water hardness.
- (b) `Mg^(2+)` and `K^(+)`: Again, potassium does not contribute to hardness.
- (c) `Ca^(2+)` and `Mg^(2+)`: Both calcium and magnesium are known to cause hardness in water.
- (d) `Ba^(2+)` and `Zn^(2+)`: Barium and zinc do not significantly contribute to water hardness.

3. **Identifying the Correct Answer**:
- The only option that includes ions known to cause water hardness is option (c) `Ca^(2+)` and `Mg^(2+)`.

4. **Conclusion**:
- Therefore, the correct answer is (c) `Ca^(2+)` and `Mg^(2+)`.

### Final Answer:
(c) `Ca^(2+)` and `Mg^(2+)`

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