What is true about ` H _ 2 S _ n O _ 6 ` ( polythionic acid ) ?

Options

A. Total S - S bond = n
B. No. of S with 'O' state = n - 1
C. No. of S with + 5 state = n - 2
D. No. of ` d _ (pi) - p _ (pi) ` bond = 4

Answer

To solve the question regarding the properties of polythionic acid \( H_2S_nO_6 \), we will analyze the structure and characteristics of the compound step by step.

### Step 1: Understanding the Structure of Polythionic Acid
Polythionic acids are a series of sulfur-containing acids. The general formula for polythionic acids can be represented as \( H_2S_nO_6 \), where \( n \) indicates the number of sulfur atoms.

### Step 2: Drawing the Structure
The structure of polythionic acid can be represented as follows:
- The central sulfur atoms are connected to each other.
- Each sulfur atom is bonded to oxygen atoms, some of which are double-bonded (S=O) and some are single-bonded (S-OH).

### Step 3: Counting S-S Bonds
In the structure of \( H_2S_nO_6 \):
- The number of S-S bonds can be calculated. If there are \( n \) sulfur atoms, the number of S-S bonds is \( n - 1 \) because each sulfur (except the terminal ones) is bonded to another sulfur.
- Therefore, the total number of S-S bonds is \( n - 1 \).

### Step 4: Oxidation States of Sulfur
- In polythionic acid, the central sulfur atoms typically have an oxidation state of 0.
- The terminal sulfur atoms connected to oxygen (with a higher oxidation state) will have a +5 oxidation state.
- Thus, if there are \( n \) sulfur atoms, the number of sulfur atoms with a zero oxidation state is \( n - 1 \) (the central sulfur), and the number with a +5 oxidation state is 2 (the terminal sulfur atoms).

### Step 5: Counting dπ-pπ Bonds
- The sulfur atoms can form dπ-pπ bonds with the oxygen atoms due to the presence of empty d orbitals in sulfur and filled p orbitals in oxygen.
- This type of bonding is significant in the structure of polythionic acids.

### Conclusion
Based on the analysis:
- The statement regarding the total number of S-S bonds being \( n \) is false; it should be \( n - 1 \).
- The statement regarding the total number of sulfur atoms with zero oxidation state is also false; it should be \( n - 1 \).
- The statement regarding the number of sulfur atoms with +5 oxidation state is false; it should be 2.
- The statement about the presence of dπ-pπ bonds is true.

Thus, the correct statement about \( H_2S_nO_6 \) (polythionic acid) is that it has dπ-pπ bonding.