In the following reaction `HCO_3^(-)+H_2OhArrCO_3^(2-)+H_3O^+` which two substances are Bronsted base ?

Options

A. `CO_3^(2-) and H_3O^+`
B. `HCO_3^- and H_3O^+`
C. `HCO_3^- and CO_3^(2-)`
D. `CO_3^(2-) and H_2O`

Answer

To determine which two substances are Bronsted bases in the reaction:

\[ \text{HCO}_3^{-} + \text{H}_2\text{O} \rightleftharpoons \text{CO}_3^{2-} + \text{H}_3\text{O}^{+} \]

we need to understand the definitions of Bronsted acids and bases.

### Step 1: Identify Bronsted Bases
A Bronsted base is defined as a substance that can accept a proton (H⁺).

### Step 2: Analyze the Reaction
1. **Bicarbonate Ion (HCO₃⁻)**: In the reaction, bicarbonate donates a proton to water, forming carbonate (CO₃²⁻) and hydronium ion (H₃O⁺). Since it donates a proton, it acts as a Bronsted acid, not a base.

2. **Water (H₂O)**: Water accepts a proton from bicarbonate, forming hydronium (H₃O⁺). Since it accepts a proton, it acts as a Bronsted base.

3. **Carbonate Ion (CO₃²⁻)**: In the reverse reaction, carbonate can accept a proton to form bicarbonate (HCO₃⁻). Therefore, it also acts as a Bronsted base.

4. **Hydronium Ion (H₃O⁺)**: In the reverse reaction, hydronium can donate a proton, making it a Bronsted acid.

### Conclusion
From the analysis, the two substances that act as Bronsted bases in the reaction are:
- Water (H₂O)
- Carbonate Ion (CO₃²⁻)

### Final Answer
The two Bronsted bases in the reaction are:
- Water (H₂O)
- Carbonate Ion (CO₃²⁻)