Which one of the following molecules contains no `pi` - bond ?

Options

A. `NO_(2)`
B. `CO_(2)`
C. `H_(2)O`
D. `SO_(2).`

Explanation

To determine which of the given molecules contains no pi bonds, we need to analyze each option provided:

1. **NO2 (Nitrogen Dioxide)**:
- The nitrogen atom in NO2 has one lone pair and forms two bonds with oxygen, one of which is a double bond (which consists of one sigma bond and one pi bond). Therefore, NO2 contains pi bonds.

2. **CO2 (Carbon Dioxide)**:
- In CO2, the carbon atom forms two double bonds with the two oxygen atoms. Each double bond consists of one sigma bond and one pi bond. Hence, CO2 also contains pi bonds.

3. **H2O (Water)**:
- In H2O, the oxygen atom forms two single bonds with two hydrogen atoms. Each bond is a sigma bond and there are no double or triple bonds present. Therefore, H2O contains no pi bonds.

4. **SO2- (Sulfite Ion)**:
- In the sulfite ion, sulfur is bonded to three oxygen atoms, one of which is typically a double bond (which includes a pi bond). Thus, SO2- contains pi bonds.

Based on this analysis, the molecule that contains no pi bond is **H2O**.

### Step-by-Step Solution:
1. **Identify the molecules**: List the given options: NO2, CO2, H2O, SO2-.
2. **Analyze NO2**: Check for pi bonds. NO2 has a double bond (1 pi bond).
3. **Analyze CO2**: Check for pi bonds. CO2 has two double bonds (2 pi bonds).
4. **Analyze H2O**: Check for pi bonds. H2O has only single bonds (0 pi bonds).
5. **Analyze SO2-**: Check for pi bonds. SO2- has at least one double bond (1 pi bond).
6. **Conclusion**: The only molecule with no pi bonds is H2O.