Which of the following equations is correct ?

Options

A. `CO_(2) rarr H_(2)CO_(3) rarr HCO_(3)^(-) + H^(+)`
B. `CO_(2) + H_(2)O overset("Carbonic")underset("anhydrase")hArrH_(2)C_(3)overset("Carbone")underset("anhydrase")hArrH^(+) + HCO_(3)^(-)`
C. `CO_(2) + H_(2)O rArr CH_(4) + 2O_(2)`
D. `CO_(2) + H_(2)O hArr CO + H_(2)O_(2)`

Answer

To determine which of the provided equations is correct, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Evaluate the First Equation:**
- The first equation states that carbon dioxide (CO2) gives carbonic acid (H2CO3), which dissociates into bicarbonate (HCO3-) and hydrogen ions (H+).
- This reaction can be represented as:
\[ CO2 + H2O \rightleftharpoons H2CO3 \rightleftharpoons HCO3^- + H^+ \]
- This equation is correct because carbon dioxide reacts with water to form carbonic acid, which then dissociates into bicarbonate and hydrogen ions.

2. **Evaluate the Second Equation:**
- The second equation suggests that carbon dioxide reacts with water to form H2C3 (which is not a standard chemical notation).
- The correct reaction is:
\[ CO2 + H2O \rightleftharpoons H2CO3 \]
- Therefore, this equation is incorrect as it incorrectly represents the formation of H2C3.

3. **Evaluate the Third Equation:**
- The third equation states that carbon dioxide and water react to form methane (CH4) and oxygen (O2).
- This reaction does not occur under normal biological conditions. Instead, methane is produced from anaerobic digestion or fermentation processes, and the combustion of methane produces carbon dioxide and water:
\[ CH4 + 2O2 \rightarrow CO2 + 2H2O \]
- Thus, this equation is also incorrect.

4. **Evaluate the Fourth Equation:**
- The fourth equation states that carbon dioxide and water will form carbon monoxide (CO) and hydrogen peroxide (H2O2).
- This reaction is not a standard or recognized reaction in biological systems. Carbon monoxide is typically produced from incomplete combustion, and hydrogen peroxide is not formed from the direct reaction of CO2 and H2O.
- Therefore, this equation is incorrect.

### Conclusion:
After evaluating all the equations, the first equation is the only correct one:
\[ CO2 + H2O \rightleftharpoons H2CO3 \rightleftharpoons HCO3^- + H^+ \]