Point out the difference between London dispersion forces and dipole-dipole forces.

Explanation

### Step-by-Step Solution:

1. **Definition of Forces**:
- **Dipole-Dipole Forces**: These are attractive forces that occur between molecules that have permanent dipoles, meaning they are polar. A permanent dipole arises from the uneven distribution of electron density between atoms in a molecule, leading to regions of partial positive and negative charge.
- **London Dispersion Forces**: These are weak intermolecular forces that exist between all molecules, whether they are polar or non-polar. They arise due to temporary fluctuations in electron density that create instantaneous dipoles, which induce dipoles in neighboring molecules.

2. **Nature of Molecules**:
- **Dipole-Dipole Forces**: Operate specifically in polar molecules. For example, hydrogen chloride (HCl) exhibits dipole-dipole interactions because of the difference in electronegativity between hydrogen and chlorine, resulting in a permanent dipole.
...