The reactivity of xenon is attributed to 

Options

A. small atomic size of xenon
B. highest heat of vapourisation
C. lower ionisation potential
D. higher ratio of molar heat capacities

Answer

To determine the reason for the reactivity of xenon, we need to analyze the provided options and understand the properties of xenon as a noble gas.

### Step-by-Step Solution:

1. **Understanding Noble Gases**:
- Noble gases, including xenon, are known for their lack of reactivity under normal conditions due to their complete valence electron shells.

2. **Analyzing the Options**:
- **Option 1: Atomic size of xenon is small**:
- This is incorrect. Xenon is one of the larger noble gases, and its atomic size is relatively large compared to other noble gases.

- **Option 2: Highest heat of vaporization**:
- This option is not relevant to reactivity. Heat of vaporization relates to the energy required to convert a substance from liquid to gas, not its chemical reactivity.

- **Option 3: Lower ionization potential**:
- As we move down the group of noble gases, the atomic size increases, leading to a decrease in ionization energy. Lower ionization energy means that it is easier to remove an electron from xenon, which can lead to the formation of compounds.

- **Option 4: Higher ratio of molar heat capacity**:
- Similar to option 2, this does not relate to chemical reactivity.

3. **Conclusion**:
- The reactivity of xenon is primarily attributed to its lower ionization potential. This allows xenon to react with highly electronegative elements like oxygen and fluorine to form xenon oxides and fluorides.

### Final Answer:
The reactivity of xenon is attributed to **lower ionization potential**.

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