Water can act as

Options

A. an acid
B. base
C. reductant
D. oxidant

Answer

### Step-by-Step Solution:

1. **Understanding Water's Properties**: Water (H₂O) is a unique molecule that can act in multiple roles in chemical reactions due to its ability to donate and accept protons (H⁺ ions) and its redox properties.

2. **Water as an Acid**: Water can act as an acid because it can donate a proton (H⁺). When water donates a proton, it forms hydroxide ions (OH⁻). This behavior aligns with the Brønsted-Lowry definition of acids.

- **Reaction**: H₂O → H⁺ + OH⁻

3. **Water as a Base**: Water can also act as a base because it can accept a proton (H⁺). When water accepts a proton, it forms hydronium ions (H₃O⁺). This is also consistent with the Brønsted-Lowry definition, where a base is a proton acceptor.

- **Reaction**: H₂O + H⁺ → H₃O⁺

4. **Water as a Reductant**: Water can act as a reductant (reducing agent) in certain reactions. In a redox reaction, it can donate electrons, which can lead to the reduction of another species.

- **Example Reaction**: 6HF + O₂ → 3H₂O + 3F₂
- Here, water is involved in a reaction where it donates electrons, thus acting as a reductant.

5. **Water as an Oxidant**: Water can also function as an oxidant (oxidizing agent) in some reactions. In this case, it can accept electrons, leading to the oxidation of another species.

- **Example Reaction**: C + H₂O → CO + H₂
- In this reaction, water accepts electrons, thus acting as an oxidant.

6. **Conclusion**: Based on the above analysis, we can conclude that water can act as:
- An acid (donates H⁺)
- A base (accepts H⁺)
- A reductant (donates electrons)
- An oxidant (accepts electrons)

### Final Answer:
Water can act as an acid, base, reductant, and oxidant.

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