Consider the following reaction,
(i) `CO_(3)^(2-)+H_(2)OhArrHCO_(3)^(-)+OH^(-)`
(ii) `CO_(2)+H_(2)OhArrH_(2)CO_(3)`
(iii) `NH_(3)+H_(2)OhArrNH_(4)OH`
(iv) `HCl+H_(2)OhArrCl^(-)+H_(3)O^(+)`
Which of the pairs of reaction proves that water is amphoteric in character?

Options

A. (i) and (ii)
B. (ii) and (iii)
C. (iii) and (iv)
D. (i) and (iii)

Answer

To determine which pairs of reactions prove that water is amphoteric in character, we need to analyze each reaction to see how water behaves in them. An amphoteric substance can act as both an acid and a base.

### Step-by-Step Solution:

1. **Analyze Reaction (i)**:
\[ \text{CO}_3^{2-} + \text{H}_2\text{O} \rightleftharpoons \text{HCO}_3^{-} + \text{OH}^{-} \]
- In this reaction, water acts as an acid because it donates a proton (H⁺) to the carbonate ion (CO₃²⁻), forming bicarbonate (HCO₃⁻) and hydroxide ion (OH⁻).

2. **Analyze Reaction (ii)**:
\[ \text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 \]
- Here, water acts as a base because it accepts a proton from carbon dioxide (CO₂) to form carbonic acid (H₂CO₃).

3. **Analyze Reaction (iii)**:
\[ \text{NH}_3 + \text{H}_2\text{O} \rightleftharpoons \text{NH}_4\text{OH} \]
- In this reaction, water acts as an acid because it donates a proton to ammonia (NH₃), forming ammonium hydroxide (NH₄OH).

4. **Analyze Reaction (iv)**:
\[ \text{HCl} + \text{H}_2\text{O} \rightleftharpoons \text{Cl}^{-} + \text{H}_3\text{O}^{+} \]
- In this case, water acts as a base because it accepts a proton from hydrochloric acid (HCl), forming hydronium ion (H₃O⁺) and chloride ion (Cl⁻).

### Conclusion:
From the analysis, we can see that:
- In reactions (ii) and (iii), water acts as both an acid and a base:
- In (ii), it acts as a base.
- In (iii), it acts as an acid.

Thus, the pairs of reactions that prove that water is amphoteric in character are **(ii) and (iii)**.