How many `pi-bonds` are present in Marshall's acid ?

Explanation

To determine the number of pi bonds present in Marshall's acid (peroxydisulfuric acid, H2S2O8), we can follow these steps:

### Step 1: Write the Molecular Formula
The molecular formula of Marshall's acid is H2S2O8.

### Step 2: Draw the Lewis Structure
To find the number of pi bonds, we need to draw the Lewis structure of H2S2O8. The structure can be represented as follows:
- Start with the sulfur (S) atoms in the center.
- Connect the sulfur atoms with single bonds.
- Attach hydroxyl (OH) groups to each sulfur atom.
- Connect oxygen (O) atoms with double bonds to the sulfur atoms.

The structure can be visualized as:
```
OH
|
O=S=O
|
O-S-OH
```
Where the S=O represents double bonds and the S-O represents single bonds.

### Step 3: Identify the Bonds
In the structure:
- Each double bond (S=O) contains one sigma bond and one pi bond.
- Each single bond (S-O or O-H) contains only sigma bonds.

### Step 4: Count the Pi Bonds
From the Lewis structure:
- There are four double bonds (two between sulfur and oxygen, and two between sulfur and the other oxygen).
- Each double bond contributes one pi bond.

Thus, we count:
- 1 pi bond from the first S=O
- 1 pi bond from the second S=O
- 1 pi bond from the third S=O
- 1 pi bond from the fourth S=O

### Conclusion
In total, there are 4 pi bonds present in Marshall's acid (H2S2O8).

**Final Answer: 4 pi bonds**

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