Which of the following oxoacids of sulphur has peroxide linkage ?

Question

Accepted Answer

The correct answer is Option 3: $H_{2}S_{2}O_{8}$, which is known as peroxodisulfuric acid. This oxoacid of sulfur is characterized by the presence of a peroxide linkage. Let's delve into the details to understand why this is the case and why the other options do not have a peroxide linkage.

1. **Explanation for Option 3 ($H_{2}S_{2}O_{8}$):**
   - Peroxodisulfuric acid, $H_{2}S_{2}O_{8}$, contains a peroxide linkage, which is an -O-O- bond. This is a distinctive feature of this acid, setting it apart from other sulfur oxoacids. The structure of $H_{2}S_{2}O_{8}$ includes two sulfur atoms, each bonded to four oxygen atoms, with one of the oxygen atoms forming a bridge between the two sulfur atoms through a peroxide linkage. This peroxide linkage is what qualifies $H_{2}S_{2}O_{8}$ as the correct answer.

2. **Explanation for why other options are incorrect:**

- **Option 1 ($H_{2}SO_{3}$):**
     - $H_{2}SO_{3}$ is known as sulfurous acid. It does not contain a peroxide linkage. Instead, it consists of a sulfur atom bonded to three oxygen atoms, with one of the oxygen atoms forming a double bond with sulfur and the other two forming single bonds. There is no -O-O- bond present in this structure.

- **Option 2 ($H_{2}SO_{4}$):**
     - $H_{2}SO_{4}$ is sulfuric acid. Similar to sulfurous acid, it does not have a peroxide linkage. The structure of sulfuric acid includes a sulfur atom bonded to four oxygen atoms, with two of them forming double bonds and the other two forming single bonds with hydrogen atoms. Again, there is no -O-O- bond in this structure.

- **Option 4 ($H_{2}S_{2}O_{7}$):**
     - $H_{2}S_{2}O_{7}$ is known as pyrosulfuric acid or oleum. This acid consists of two sulfur atoms, each bonded to four oxygen atoms, with one oxygen atom forming a bridge between the two sulfur atoms. However, this bridging oxygen does not form a peroxide linkage; it is a simple oxygen bridge without the -O-O- bond characteristic of a peroxide linkage.

In conclusion, $H_{2}S_{2}O_{8}$ is the only oxoacid among the given options that contains a peroxide linkage, making Option 3 the correct answer.