Why are only `Pb^(2+),Ag^(o+)` and `Hg_(2)^(2+)` ions precipitated in group I?

Explanation

To understand why only \( \text{Pb}^{2+}, \text{Ag}^{+}, \) and \( \text{Hg}_2^{2+} \) ions are precipitated in Group I during qualitative inorganic salt analysis, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Group I Cations**:
Group I cations in qualitative analysis are specifically \( \text{Pb}^{2+} \) (lead), \( \text{Ag}^{+} \) (silver), and \( \text{Hg}_2^{2+} \) (mercury). These ions are known for forming insoluble chlorides when treated with hydrochloric acid (HCl).

2. **Reagent Used**:
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