The compound that cannot be formed by xenon is:

Options

A. `XeO_(3)`
B. `XeF_(4)`
C. `XeCl_(4)`
D. `XeO_(2)F_(2)`

Answer

To determine which compound cannot be formed by xenon, we will analyze each of the given options: XeO3, XeF4, XeCl4, and XeO2F2.

### Step-by-Step Solution:

1. **Understanding Xenon's Chemistry**:
- Xenon is a noble gas and can form compounds due to its ability to expand its octet. It can form compounds with highly electronegative elements.

2. **Analyzing the Options**:
- **XeO3**: This compound is xenon trioxide. Xenon can form oxides, and XeO3 is a known compound.
- **XeF4**: This is xenon tetrafluoride. Xenon can form stable compounds with fluorine due to its small size and high electronegativity. XeF4 is also a known compound.
- **XeCl4**: This is xenon tetrachloride. Here, we need to consider the size of chlorine. Chlorine is larger than fluorine, which may affect the ability of xenon to bond with it effectively.
- **XeO2F2**: This is a mixed oxide-fluoride of xenon. Xenon can form such compounds as it can bond with both oxygen and fluorine.

3. **Comparing Sizes**:
- The size difference between xenon and its bonding partners is crucial. For stable compounds, the neighboring atoms should ideally be smaller than xenon to allow for effective bonding.
- Fluorine is smaller than chlorine, which allows xenon to form stable compounds with fluorine (like XeF4) but poses a challenge with larger atoms like chlorine.

4. **Conclusion**:
- Given the analysis, xenon can form XeO3, XeF4, and XeO2F2. However, due to the larger size of chlorine compared to xenon, it cannot effectively form XeCl4. Therefore, the compound that cannot be formed by xenon is **XeCl4**.

### Final Answer:
The compound that cannot be formed by xenon is **XeCl4** (Option 3).