Which factor is most responsible for the increase in boiling points of noble gases from He to Xe?

Options

A. Decrease in I.E.
B. Monoatomic nature
C. Decrease in polarisability
D. Increase in polarisability

Answer

To determine which factor is most responsible for the increase in boiling points of noble gases from Helium (He) to Xenon (Xe), we can analyze the options provided and understand the underlying principles.

### Step-by-Step Solution:

1. **Understanding Noble Gases**: Noble gases are located in Group 18 of the periodic table and include Helium, Neon, Argon, Krypton, Xenon, and Radon. They are known for their low reactivity and exist as monatomic gases.

2. **Boiling Points Trend**: As we move down the group from Helium to Xenon, we observe an increase in boiling points. For example, Helium has a boiling point of -269°C, while Xenon has a boiling point of -108°C.

3. **Analyzing the Options**:
- **Option 1: Decrease in Ionization Energy**: While ionization energy does decrease down the group, it is not the primary factor affecting boiling points.
- **Option 2: Monatomic Nature**: All noble gases are monatomic, so this factor does not explain the trend in boiling points.
- **Option 3: Decrease in Polarizability**: This is incorrect since polarizability actually increases down the group.
- **Option 4: Increase in Polarizability**: As we move from He to Xe, the number of electrons increases, which leads to greater polarizability. Larger atoms can have their electron clouds distorted more easily, leading to stronger London dispersion forces.

4. **Conclusion**: The increase in polarizability is the most significant factor responsible for the increase in boiling points of noble gases from Helium to Xenon. As the atomic size increases, the polarizability increases, resulting in stronger intermolecular forces and thus higher boiling points.

### Final Answer:
The factor most responsible for the increase in boiling points of noble gases from He to Xe is **increase in polarizability** (Option 4).