What is meant by 'demineralised water' and how it can be obtained?

Options

A. Water free from cations and anions.
B. Water free from minerals dissolved in it.
C. Water free from impurities.
D. Water free from `Na^(+)` and `K^(+)` ions.

Explanation

**Step-by-Step Solution:**

1. **Definition of Demineralised Water**: Demineralised water is water that has had its mineral ions removed. This includes both cations (positively charged ions) and anions (negatively charged ions). Essentially, it is water that is free from dissolved minerals and salts.

2. **Understanding Impurities**: In natural water sources, various minerals and impurities are typically present. These can include calcium, magnesium, sodium, potassium, chloride, sulfate, and bicarbonate ions, among others.

3. **Characteristics of Demineralised Water**: For water to be classified as demineralised, it must be devoid of these dissolved minerals and salts. This means that it should not contain any significant concentrations of cations or anions.

4. **Methods of Obtaining Demineralised Water**: Demineralised water can be obtained through several methods, including:
- **Distillation**: Boiling water to produce steam and then condensing the steam back into liquid water, leaving impurities behind.
- **Ion Exchange**: Passing water through a resin that exchanges the mineral ions for hydrogen and hydroxide ions, effectively removing them.
- **Reverse Osmosis**: Forcing water through a semi-permeable membrane that allows only water molecules to pass while blocking larger ions and impurities.

5. **Conclusion**: Therefore, demineralised water is defined as water that is free from dissolved minerals and salts, and it can be obtained through processes such as distillation, ion exchange, or reverse osmosis.

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