The correct statement is

Options

A. Diamond is covalent yet it has high melting point
B. `[SiF_(6)]^(2-)` is known whereas `[SiCl_(6)]^(2-)` is not
C. `SiO` only exist at high temp
D. All of these

Answer

To determine the correct statement among the provided options, we will analyze each statement step by step.

### Step 1: Analyze Option 1
**Statement:** "Diamond is covalent yet it has a high melting point."

**Explanation:**
- Diamond has a covalent network structure, which consists of strong covalent bonds throughout the entire structure.
- High melting points are characteristic of materials with strong bonds because a significant amount of energy is required to break these bonds.
- Therefore, this statement is correct.

### Step 2: Analyze Option 2
**Statement:** "SiF6 (silicon hexafluoride) exists, but SiCl6 (silicon hexachloride) does not."

**Explanation:**
- Silicon can form a stable compound with fluorine (SiF6) due to the small size of fluorine, which allows it to accommodate around silicon effectively.
- However, chlorine is larger, and the interaction between silicon and chlorine is less favorable, making SiCl6 unstable or non-existent.
- Thus, this statement is also correct.

### Step 3: Analyze Option 3
**Statement:** "SiO (silicon monoxide) only exists at high temperature."

**Explanation:**
- Silicon monoxide (SiO) is indeed unstable at room temperature and tends to decompose into silicon and silicon dioxide (SiO2) unless maintained at high temperatures.
- The formation of SiO is an endothermic process, requiring high energy, which is why it is only stable at elevated temperatures.
- Therefore, this statement is correct.

### Step 4: Analyze Option 4
**Statement:** "All of these statements are correct."

**Explanation:**
- Since we have established that Options 1, 2, and 3 are all correct, this statement must also be correct.

### Conclusion
The correct answer is Option 4: "All of these statements are correct."

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