Which of the following has the highest boiling point?

Options

A. `CH_4 `
B. `He `
C. `H_2 `
D. Xe

Answer

To determine which of the following substances has the highest boiling point among CH4 (methane), He (helium), H2 (hydrogen), and U (uranium), we need to analyze the types of intermolecular forces present in each substance and their molecular masses.

### Step-by-Step Solution:

1. **Identify the Substances and Their Properties**:
- CH4 (methane): A covalent compound with weak Van der Waals forces.
- He (helium): A noble gas with very weak Van der Waals forces.
- H2 (hydrogen): A diatomic molecule with weak Van der Waals forces.
- U (uranium): A metallic element with strong metallic bonds.

2. **Understand Intermolecular Forces**:
- **Covalent Bonds**: Strong bonds found within molecules (e.g., in CH4).
- **Van der Waals Forces**: Weak forces present in noble gases and non-polar molecules.
- **Metallic Bonds**: Strong bonds found in metals (e.g., in uranium).

3. **Compare Molecular Masses**:
- CH4: Molecular mass = 16 g/mol
- He: Atomic mass = 4 g/mol
- H2: Molecular mass = 2 g/mol
- U: Atomic mass = 238 g/mol

4. **Analyze Boiling Points Based on Forces and Mass**:
- The boiling point of a substance is influenced by both the strength of its intermolecular forces and its molecular mass.
- CH4 has weak Van der Waals forces and a low molecular mass.
- He and H2 have even weaker forces and lower molecular masses.
- Uranium, being a metal, has strong metallic bonds and a significantly higher molecular mass.

5. **Conclusion**:
- Among the given substances, uranium (U) has the highest boiling point due to its strong metallic bonds and high atomic mass.

### Final Answer:
**Uranium (U) has the highest boiling point among CH4, He, H2, and U.**