Which of the following have X-O-X linkage ?
(where X is central atom):
(i)`Cr_(2)O_(7)^(2-)` (ii)`S_(2)O_(3)^(2-)` (iii) pyrosilicate (iv) Hyponitrous acid

Options

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

Explanation

To determine which of the given compounds have an X-O-X linkage (where X is the central atom), we will analyze each option step by step.

### Step 1: Analyze `Cr2O7^(2-)`
- The compound is the dichromate ion.
- The structure consists of two chromium (Cr) atoms and seven oxygen (O) atoms.
- The bonding can be represented as:
- Each chromium is bonded to three oxygen atoms, and there are two bridging oxygen atoms between the chromium atoms.
- The structure can be visualized as:
```
O
|
O--Cr--O
|
Cr
|
O
```
- This shows that there are Cr-O-Cr linkages, which can be interpreted as X-O-X linkages where X is Cr.
- **Conclusion**: `Cr2O7^(2-)` has X-O-X linkage.

### Step 2: Analyze `S2O3^(2-)`
- The compound is the thiosulfate ion.
- The structure consists of two sulfur (S) atoms and three oxygen (O) atoms.
- The bonding can be represented as:
- One sulfur is bonded to the other sulfur and to two oxygen atoms.
- The structure can be visualized as:
```
O
|
O--S--S
```
- There are no direct S-O-S linkages; instead, the linkages are S-O.
- **Conclusion**: `S2O3^(2-)` does not have X-O-X linkage.

### Step 3: Analyze Pyrosilicate
- The compound is represented as `Si2O7`.
- The structure consists of two silicon (Si) atoms and seven oxygen (O) atoms.
- The bonding can be represented as:
- Each silicon is bonded to four oxygen atoms, and the oxygen atoms are shared between the silicon atoms.
- The structure can be visualized as:
```
O
|
O--Si--O
|
Si
|
O
```
- This shows that there are Si-O-Si linkages, which can be interpreted as X-O-X linkages where X is Si.
- **Conclusion**: Pyrosilicate has X-O-X linkage.

### Step 4: Analyze Hyponitrous Acid
- The compound is represented as `N2O2H2`.
- The structure consists of two nitrogen (N) atoms and two oxygen (O) atoms.
- The bonding can be represented as:
- The nitrogen atoms are bonded to each other and to hydroxyl (OH) groups.
- The structure can be visualized as:
```
OH
|
N--N
|
OH
```
- There are no direct N-O-N linkages; instead, the linkages are N-O.
- **Conclusion**: Hyponitrous acid does not have X-O-X linkage.

### Final Answer:
The compounds that have X-O-X linkage are:
1. `Cr2O7^(2-)`
2. Pyrosilicate