In how many solids only london dispersion forces exist ? Dry ice, Ice, Solid `I_(2)`, Solid 'Xe', Rocksalt, 'He' gas

Answer

To determine how many solids exhibit only London dispersion forces among the given substances, we need to analyze each substance based on its molecular characteristics.

### Step-by-Step Solution:

1. **Identify the substances**: The substances given are:
- Dry ice (solid CO₂)
- Ice (solid H₂O)
- Solid I₂
- Solid Xe
- Rock salt (NaCl)
- Helium gas (He)

2. **Determine the nature of each substance**:
- **Dry ice (solid CO₂)**: CO₂ is a nonpolar molecule because it has a linear structure, and the dipole moments cancel out. Therefore, it exhibits only London dispersion forces.
- **Ice (solid H₂O)**: Water is a polar molecule due to the presence of hydrogen bonding. Thus, it does not only exhibit London dispersion forces.
- **Solid I₂**: I₂ is a nonpolar molecule, and it exhibits only London dispersion forces.
- **Solid Xe**: Xenon (Xe) is a noble gas and is nonpolar. It also exhibits only London dispersion forces.
- **Rock salt (NaCl)**: Rock salt is an ionic compound, and it does not exhibit London dispersion forces; instead, it has ionic bonds.
- **Helium gas (He)**: Helium is a nonpolar noble gas, and in its solid state, it exhibits only London dispersion forces.

3. **Count the solids that exhibit only London dispersion forces**:
- Dry ice (CO₂) - Yes
- Solid I₂ - Yes
- Solid Xe - Yes
- Rock salt (NaCl) - No
- Helium gas (He) - Yes (in solid state)

4. **Final Count**: The solids that exhibit only London dispersion forces are:
- Dry ice (CO₂)
- Solid I₂
- Solid Xe
- Helium (in solid state)

Thus, there are **4 solids** that exhibit only London dispersion forces.

### Final Answer:
**4 solids exhibit only London dispersion forces.**