Which one of the following molecules does not possess a permanent electric dipole moment?

Options

A. `H_2 S `
B. `SO_2`
C. `CS_2`
D. `SO_3`

Explanation

To determine which molecule does not possess a permanent electric dipole moment among the given options (H2S, SO2, CH2, and SO3), we can analyze each molecule's structure and the electronegativity of its constituent atoms.

### Step-by-Step Solution:

1. **Understanding Electric Dipole Moment**:
- An electric dipole moment occurs when there is a separation of positive and negative charges in a molecule. A molecule has a permanent dipole moment if it has a net dipole due to its shape and the electronegativity differences between its atoms.

2. **Analyzing H2S**:
- H2S has a bent molecular geometry.
- Sulfur (S) is more electronegative than hydrogen (H), leading to a dipole moment directed towards sulfur.
- The two dipoles do not cancel out due to the bent shape, resulting in a non-zero dipole moment.

3. **Analyzing SO2**:
- SO2 also has a bent structure.
- Oxygen (O) is more electronegative than sulfur (S), creating dipoles directed towards the oxygen atoms.
- The dipoles do not cancel out, leading to a non-zero dipole moment.

4. **Analyzing CH2 (assuming it refers to CH2Cl2 or a similar compound)**:
- If we consider CH2 as a linear molecule (like carbon dioxide), it would have a symmetrical structure.
- The electronegativity difference between carbon (C) and hydrogen (H) is very small, and the dipoles from the C-H bonds would cancel each other out.
- Therefore, CH2 has a net dipole moment of zero.

5. **Analyzing SO3**:
- SO3 has a trigonal planar structure.
- The dipoles from the S-O bonds are equal and symmetrically arranged, leading to cancellation of the dipoles.
- Thus, SO3 also has a net dipole moment of zero.

6. **Conclusion**:
- From the analysis, both CH2 and SO3 do not possess a permanent electric dipole moment. However, if we consider CH2 as a linear molecule, it will have a net dipole moment of zero. Therefore, the answer to the question is that CH2 and SO3 do not possess a permanent electric dipole moment.

### Final Answer:
CH2 and SO3 do not possess a permanent electric dipole moment.