Which of the following pairs contain molecular solids but different nature of intermolecular forces?

Options

A. Ice, `NaCl`
B. `NaCl, KCl`
C. `SiO_(2),` graphite
D. Ice and dry ice

Explanation

To solve the question, "Which of the following pairs contain molecular solids but different nature of intermolecular forces?", we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Molecular Solids**:
- Molecular solids are solids that are composed of molecules held together by intermolecular forces. These forces can include hydrogen bonding, dipole-dipole interactions, and van der Waals forces.

2. **Analyzing the Options**:
- **Option 1: Ice (H₂O) and NaCl**:
- Ice is a molecular solid where molecules are held together by hydrogen bonds.
- NaCl is an ionic solid, not a molecular solid. Therefore, this pair does not fit the criteria.

- **Option 2: NaCl and KCl**:
- Both NaCl and KCl are ionic solids. They consist of ions held together by ionic bonds. Thus, this pair does not contain molecular solids and is not suitable.

- **Option 3: SiO₂ and Graphite**:
- SiO₂ (silicon dioxide) has a network covalent structure, and graphite consists of layers of carbon atoms bonded covalently within layers but held together by weaker van der Waals forces between layers. Both have strong covalent bonding, so this pair does not meet the criteria of different intermolecular forces.

- **Option 4: Ice (H₂O) and Dry Ice (CO₂)**:
- Ice is a molecular solid with hydrogen bonding.
- Dry ice (solid CO₂) is a molecular solid held together by weak dispersion forces (London forces).
- Since they both are molecular solids but have different types of intermolecular forces (hydrogen bonding in ice and dispersion forces in dry ice), this pair fits the criteria.

3. **Conclusion**:
- The correct answer is **Option 4: Ice and Dry Ice**, as they are both molecular solids but have different types of intermolecular forces.