Which of the following compounds has a lone pair of electrons at the central atom ?
`H_(2)S_(2)O_(8), H_(2)S_(2)O_(7), H_(2)SO_(3), H_(2)SO_(4)`

Explanation

To determine which of the given compounds has a lone pair of electrons at the central atom, we need to analyze the molecular structures of each compound: \( H_2S_2O_8 \), \( H_2S_2O_7 \), \( H_2SO_3 \), and \( H_2SO_4 \).

### Step-by-Step Solution:

1. **Identify the central atom in each compound**:
- For \( H_2S_2O_8 \) (Peroxydisulfuric acid), the central atom is sulfur (S).
- For \( H_2S_2O_7 \) (Oleum), the central atom is also sulfur (S).
- For \( H_2SO_3 \) (Sulfurous acid), the central atom is sulfur (S).
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