In which of the following silicates, only two corners per tetrahedron are shared ?
I. Pyrosilicate
II. Cyclic silicate
III Double chain silicate
IV Single chain silicate
V 3D Silicate

Options

A. (i),(ii) and (iv)
B. (iv) and (vi) only
C. (i) and (vi) only
D. (ii) and (iv) only

Explanation

To solve the question regarding which silicates share only two corners per tetrahedron, we will analyze each type of silicate mentioned in the question step by step.

### Step 1: Understand the Types of Silicates
Silicates can be classified based on how the tetrahedra (SiO4) are arranged and how many corners are shared. The types mentioned are:
1. Pyrosilicate
2. Cyclic silicate
3. Double chain silicate
4. Single chain silicate
5. 3D Silicate

### Step 2: Analyze Each Type of Silicate
- **I. Pyrosilicate**: In pyrosilicates, each tetrahedron shares one corner with another tetrahedron. Therefore, they do not share two corners.

- **II. Cyclic Silicate**: In cyclic silicates, the tetrahedra are arranged in a ring structure, and each tetrahedron shares two corners with adjacent tetrahedra. Thus, this type shares two corners per tetrahedron.

- **III. Double Chain Silicate**: In double chain silicates, each tetrahedron shares two corners with two adjacent tetrahedra, but the overall structure allows for more complex sharing. However, it does not consistently share only two corners per tetrahedron.

- **IV. Single Chain Silicate**: In single chain silicates, each tetrahedron shares two corners with two adjacent tetrahedra, similar to cyclic silicates. Therefore, this type also shares two corners per tetrahedron.

- **V. 3D Silicate**: In three-dimensional silicates, each tetrahedron shares four corners with adjacent tetrahedra, which does not meet the criteria of sharing only two corners.

### Step 3: Conclusion
From the analysis, we find that:
- **Cyclic Silicate (II)** and **Single Chain Silicate (IV)** are the types that share only two corners per tetrahedron.

### Final Answer
The correct answer is:
**II. Cyclic Silicate and IV. Single Chain Silicate.**

---