The first compound of a noble gas known is

Options

A. `Xe.6H_2O`
B. `Xe[PtF_6]`
C. `XeO_3`
D. `XeF_6`

Answer

To determine the first compound of a noble gas, we need to analyze the options provided: XeCl2, XePtF6, XeO3, and XeF6.

### Step-by-Step Solution:

1. **Understanding Noble Gases**: Noble gases are known for their lack of reactivity due to having a complete valence shell. However, under certain conditions, they can form compounds.

2. **Analyzing the Options**:
- **XeCl2**: This is xenon dichloride, which is not the first known compound of a noble gas.
- **XePtF6**: This is xenon hexafluoroplatinate. It is known as the first compound of a noble gas.
- **XeO3**: This is xenon trioxide, but it was discovered after XePtF6.
- **XeF6**: This is xenon hexafluoride, which is also a compound of xenon but is not the first.

3. **Identifying the First Compound**: Among the options, XePtF6 is recognized as the first compound of a noble gas, specifically xenon. This compound was synthesized in the 1960s.

4. **Conclusion**: Therefore, the answer to the question is **XePtF6**, also known as xenon hexafluoroplatinate.

### Final Answer:
The first compound of a noble gas known is **XePtF6** (xenon hexafluoroplatinate).

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