The correct order of enthalpy of vaporsation of noble gases is 

Options

A. a. `Xe gt Kr gt Ar gt N e gt He`
B. b. `Xe gt Ar gt He gt N e gt KI`
C. c. `He gt N e gt Kr gt Ar gt Xe`
D. d. `Ne gt X e gt K gt He gt AI`

Answer

To determine the correct order of enthalpy of vaporization of noble gases, we need to consider the trends in the properties of these gases as we move down the group in the periodic table.

### Step-by-Step Solution:

1. **Understanding Enthalpy of Vaporization**:
- Enthalpy of vaporization is the amount of energy required to convert a substance from liquid to gas at constant temperature and pressure. For noble gases, this energy is influenced by the size of the atoms and the strength of the intermolecular forces.

2. **Trends in Noble Gases**:
- As we move down the group of noble gases (from helium to radon), the atomic size increases. This leads to an increase in the number of electrons, which enhances the London dispersion forces (a type of van der Waals force) between the atoms.

3. **Effect of Atomic Size on Enthalpy of Vaporization**:
- Larger atoms have more electrons, which results in stronger dispersion forces. Therefore, the enthalpy of vaporization increases with increasing atomic size.

4. **Order of Noble Gases**:
- The noble gases in order of increasing atomic size are:
- Helium (He)
- Neon (Ne)
- Argon (Ar)
- Krypton (Kr)
- Xenon (Xe)
- Radon (Rn) (though it's radioactive and less commonly discussed in this context)
- Based on the increasing atomic size and the corresponding increase in enthalpy of vaporization, we can establish the order.

5. **Final Order**:
- The correct order of enthalpy of vaporization from highest to lowest is:
- Xenon (Xe) > Krypton (Kr) > Argon (Ar) > Neon (Ne) > Helium (He)

### Conclusion:
Thus, the correct order of enthalpy of vaporization of noble gases is:
**Xenon > Krypton > Argon > Neon > Helium**