The name 'silica' covers an entire group of minerals, which have the general formula `SiO_(2)`, the most common of which is quartz. Quartz is a framwork silicate with `SiO_(4)` tetrahdera arranged in spirals. the spirals can turn in a clockwise or anticlockwise direction-a feature that results in there being two mirror images, optically active, varieties of quartz.
In the given following emperical formulae of silicates shared and unshared oxygen corner are same by each tetrahedron in.

Options

A. `Si_(2)O_(7)^(6 Theta)`
B. `(Si_(2)O_(5)^(2o.))_(n)`
C. `(SiO_(3)^(2o.))_(n)`
D. `SiO_(4)^(4o.)`

Answer

To solve the question regarding the empirical formulas of silicates and the shared and unshared oxygen corners in tetrahedra, we can follow these steps:

### Step-by-Step Solution

1. **Understanding Silicates**: Silicates are minerals that contain silicon and oxygen, with the general formula \( SiO_2 \). The basic unit of silicates is the tetrahedron \( SiO_4^{4-} \), where silicon is at the center and four oxygen atoms are at the corners.

2. **Types of Silicates**: Silicates can be categorized based on how the tetrahedra are arranged. The main types include:
- **Framework silicates** (e.g., quartz)
- **Chain silicates**
- **Sheet silicates**
- **Nesosilicates (or orthosilicates)**

3. **Analyzing the Given Empirical Formulas**: The question provides several empirical formulas for silicates, and we need to determine which one has the same number of shared and unshared oxygen corners.

4. **Evaluating Each Formula**:
- **Option 1: \( Si_2O_7^{6-} \)** (Pyrosilicate)
- In this structure, two \( SiO_4^{4-} \) tetrahedra share one corner. Thus, there are 3 unshared corners per tetrahedron. This results in a total of 4 corners for shared and unshared oxygen not being the same.

- **Option 2: \( Si_2O_5^{2-} \)** (Sheet silicate)
- In this structure, three corners are shared among the tetrahedra, leaving one corner unshared. This also results in a mismatch between shared and unshared corners.

- **Option 3: Chain silicate**
- In chain silicates, two oxygen atoms per tetrahedron are shared, which means there are two unshared corners. This results in an equal number of shared and unshared corners (2 shared, 2 unshared).

- **Option 4: Orthosilicate**
- Orthosilicates have discrete tetrahedra where no corners are shared. Thus, there is no sharing, leading to a mismatch.

5. **Conclusion**: The only empirical formula where the number of shared and unshared oxygen corners is the same is found in the chain silicate structure. Therefore, the correct answer is the empirical formula representing chain silicates.

### Final Answer
The empirical formula where the shared and unshared oxygen corners are the same is the one representing **chain silicates**.

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