Assertion `SiF_(6)^(2-)` anion exists but `CF_(6)^(2-)` does not
Reasoning Si atom vacnat d-orbital while C-atom has not .

Options

A. If both `(A)` and `(R )` are correct and `(R )` is the correct explanation of `(A)`
B. If both `(A)` and `(R )` are correct and `(R )` is the correct explanation of `(A)`
C. If `(A)` is correct but `(R )` is incorrect
D. If `(A)` is incorrect but `(R )` is correct

Answer

To solve the question, we need to analyze both the assertion and the reasoning provided.

### Step 1: Understanding the Assertion
The assertion states that the anion \( SiF_6^{2-} \) exists, while \( CF_6^{2-} \) does not.

### Step 2: Analyzing Silicon and Carbon
Let's look at the electronic configurations of Silicon (Si) and Carbon (C):

- **Silicon (Si)**:
- Atomic number: 14
- Electronic configuration: \( 1s^2 2s^2 2p^6 3s^2 3p^2 3d^0 \)

- **Carbon (C)**:
- Atomic number: 6
- Electronic configuration: \( 1s^2 2s^2 2p^2 \)

### Step 3: Excited State of Silicon
In the excited state, one of the electrons from the \( 3s \) orbital can be promoted to the \( 3p \) orbital, resulting in four unpaired electrons. This allows Silicon to form six bonds with fluorine atoms because it can utilize its vacant \( d \) orbitals for hybridization.

### Step 4: Hybridization of Silicon
For \( SiF_6^{2-} \):
- Hybridization: \( sp^3d^2 \)
- This hybridization allows Silicon to accommodate six fluorine atoms.

### Step 5: Excited State of Carbon
For Carbon, when it is excited, it can only promote one of its \( 2s \) electrons to the \( 2p \) orbital, leading to four unpaired electrons.

### Step 6: Hybridization of Carbon
For \( CF_6^{2-} \):
- Hybridization: \( sp^3 \)
- This hybridization can only accommodate four fluorine atoms, not six.

### Step 7: Conclusion
Thus, the assertion that \( SiF_6^{2-} \) exists while \( CF_6^{2-} \) does not is true. The reasoning that Silicon has vacant \( d \) orbitals allowing it to accommodate more electrons is also correct.

### Final Answer
Both the assertion and the reasoning are correct, and the reasoning is the correct explanation of the assertion.