Which of the following compounds is not known ?

Options

A. `KrF_(2)`
B. `XeF_(4)`
C. `XeF_(6)`
D. `ArF_(2)`.

Explanation

To determine which of the following compounds is not known, we will analyze each option provided: KRF2, XZF4, XZF6, and ARF2.

### Step 1: Analyze KRF2 (Krypton Difluoride)
- Krypton (Kr) is a noble gas that can form compounds due to its relatively low ionization energy compared to other noble gases.
- KRF2 is known and is a stable compound.

**Hint:** Check the stability and existence of compounds formed by Krypton.

### Step 2: Analyze XZF4 (Xenon Tetrafluoride)
- Xenon (Xe) is another noble gas that can form several compounds.
- XZF4 is known and is a stable compound.

**Hint:** Look for common compounds formed by Xenon.

### Step 3: Analyze XZF6 (Xenon Hexafluoride)
- Xenon can also form hexafluoride.
- XZF6 is known and is a stable compound.

**Hint:** Consider the oxidation states and known compounds of Xenon.

### Step 4: Analyze ARF2 (Argon Difluoride)
- Argon (Ar) is a noble gas that is much less reactive than Krypton and Xenon.
- ARF2 is not known to exist as Argon does not readily form compounds.

**Hint:** Reflect on the reactivity of Argon compared to other noble gases.

### Conclusion
After analyzing all the options, we find that the compound that is not known is **ARF2 (Argon Difluoride)**.

### Final Answer
The answer to the question is **ARF2**.

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