Which one of the following pairs of molecules will have permanent dipole moments for both members?

Options

A. ` SiF_4 and NO_2`
B. `NO_2 and CO_2`
C. `NO_2 and O_3`
D. `SiF_4 and CO_2`

Explanation

To determine which pair of molecules has permanent dipole moments for both members, we will analyze the molecular geometry and electronegativity of the atoms involved in each option.

### Step-by-Step Solution:

1. **Identify the Molecules in Each Pair**:
- The pairs given are:
1. SiF4 and NO2
2. NO2 and CO2
3. NO2 and Ozone (O3)
4. SiF4 and CO2

2. **Analyze SiF4**:
- **Geometry**: SiF4 has a tetrahedral shape.
- **Electronegativity**: Fluorine is highly electronegative.
- **Dipole Moment**: The individual bond dipoles (Si-F) point towards the fluorine atoms. However, due to the symmetrical tetrahedral structure, these dipoles cancel each other out.
- **Conclusion**: SiF4 has a net dipole moment of zero.

3. **Analyze NO2**:
- **Geometry**: NO2 has a bent shape due to one lone pair on nitrogen.
- **Electronegativity**: Oxygen is more electronegative than nitrogen.
- **Dipole Moment**: The bond dipoles do not cancel out because of the bent shape, resulting in a non-zero dipole moment.
- **Conclusion**: NO2 has a permanent dipole moment.

4. **Analyze CO2**:
- **Geometry**: CO2 is linear.
- **Electronegativity**: The bond dipoles (C=O) are equal and opposite.
- **Dipole Moment**: The dipoles cancel each other out.
- **Conclusion**: CO2 has a net dipole moment of zero.

5. **Analyze Ozone (O3)**:
- **Geometry**: Ozone has a bent shape.
- **Electronegativity**: There is no significant difference in electronegativity between the oxygen atoms, but the lone pair on one of the oxygen atoms creates a dipole.
- **Dipole Moment**: The dipole does not cancel out due to the bent shape.
- **Conclusion**: Ozone has a permanent dipole moment.

6. **Summarize Findings**:
- From the analysis:
- SiF4: No permanent dipole moment
- NO2: Permanent dipole moment
- CO2: No permanent dipole moment
- Ozone: Permanent dipole moment

7. **Identify the Correct Pair**:
- The only pair where both molecules have permanent dipole moments is **NO2 and Ozone (O3)**.

### Final Answer:
The correct pair of molecules that have permanent dipole moments for both members is **NO2 and Ozone (O3)**.