Enzymes are biocatalysts. They catalyse biochemical reaction. In general they reduce activation energy of reactions. Many physico-chemical processes are enzyme mediated. Some examples of enzyme mediated reactions are given below. Tick the wrong entry

Options

A. Dissolving `CO_2` in water
B. Untwining the two strands of DNA
C. Hydrolysis of sucrose
D. Formation of peptide bond

Explanation

To solve the question regarding which of the given reactions is not enzyme-mediated, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Enzymes**: Enzymes are biological catalysts that speed up biochemical reactions by lowering the activation energy required for the reaction to occur. We need to identify which of the provided reactions does not involve an enzyme.

2. **Analyzing Each Reaction**:
- **Formation of Peptide Bond**: This reaction is catalyzed by an enzyme known as peptidyl transferase, which is an RNA-based enzyme. Therefore, this is an enzyme-mediated reaction.

- **Hydrolysis of Sucrose**: The enzyme that catalyzes the hydrolysis of sucrose into glucose and fructose is called sucrase or invertase. This reaction is also enzyme-mediated.

- **Untwining the Two Strands of DNA**: This process is facilitated by the enzyme DNA helicase, which unwinds the DNA strands during replication. Hence, this is another enzyme-mediated reaction.

- **Dissolving CO2 in Water**: When carbon dioxide dissolves in water, it forms carbonic acid through a simple physical process. This reaction does not require any biological catalyst or enzyme. Therefore, this is not an enzyme-mediated reaction.

3. **Identifying the Wrong Entry**: Based on the analysis, the reaction that does not involve an enzyme is the **dissolving of CO2 in water**.

### Conclusion:
The wrong entry among the examples of enzyme-mediated reactions is **dissolving CO2 in water**.

---