In which of the following molecules, intermolecular attraction is purely London force?

Options

A. `CHCl_3`
B. `CH_2Cl_2`
C. `C Cl_4`
D. `CH_3Cl`

Answer

To determine which of the given molecules has intermolecular attraction that is purely London force, we need to analyze each molecule for its polarity and the types of intermolecular forces present.

### Step-by-Step Solution:

1. **Understanding London Forces**:
- London dispersion forces (or London forces) are weak intermolecular forces that arise due to temporary dipoles in non-polar molecules. They occur when the electron distribution around a molecule becomes asymmetrical, leading to a temporary dipole that can induce dipoles in neighboring molecules.

2. **Analyzing Each Molecule**:
- **Option 1: CHCl3 (Chloroform)**:
- Structure: One carbon atom bonded to one hydrogen and three chlorine atoms.
- Polarity: Chlorine is more electronegative than hydrogen and carbon, leading to a net dipole moment. Therefore, CHCl3 is a polar molecule.
- Intermolecular Forces: Predominantly dipole-dipole interactions, with some London forces present.
- Conclusion: Not purely London forces.

- **Option 2: CH2Cl2 (Dichloromethane)**:
- Structure: One carbon atom bonded to two hydrogen atoms and two chlorine atoms.
- Polarity: The bond dipoles do not cancel out, resulting in a net dipole moment. Thus, CH2Cl2 is also a polar molecule.
- Intermolecular Forces: Dominantly dipole-dipole interactions, with some London forces.
- Conclusion: Not purely London forces.

- **Option 3: CCl4 (Carbon Tetrachloride)**:
- Structure: One carbon atom bonded to four chlorine atoms in a tetrahedral shape.
- Polarity: The symmetrical arrangement of identical chlorine atoms means that the bond dipoles cancel each other out, resulting in no net dipole moment. Therefore, CCl4 is a non-polar molecule.
- Intermolecular Forces: The only intermolecular forces present are London dispersion forces.
- Conclusion: This molecule has purely London forces.

- **Option 4: CH3Cl (Methyl Chloride)**:
- Structure: One carbon atom bonded to three hydrogen atoms and one chlorine atom.
- Polarity: The bond dipoles do not cancel out, resulting in a net dipole moment. Thus, CH3Cl is a polar molecule.
- Intermolecular Forces: Predominantly dipole-dipole interactions, with some London forces.
- Conclusion: Not purely London forces.

3. **Final Conclusion**:
- Among the options analyzed, only **CCl4** (Option 3) has intermolecular attraction that is purely London force.

### Answer:
**CCl4 (Option 3)**