The first group reagent is dil HCI, which of the following do not belong to group l?

Options

A. `Ag^(o+)`
B. `Pb^(2+)`
C. `Hg_(2)^(2+)`
D. `Cd^(2-)`

Answer

To determine which of the following cations do not belong to Group I when the first group reagent is dilute HCl, we need to analyze the behavior of each cation in the presence of dilute HCl.

### Step-by-Step Solution:

1. **Identify the Cations**: The cations given in the question are:
- Ag⁺ (Silver ion)
- Pb²⁺ (Lead ion)
- Hg₂²⁺ (Mercury(I) ion)
- Cd²⁺ (Cadmium ion)

2. **Understand Group I Cations**: Group I cations are characterized by their ability to form insoluble chlorides when treated with dilute HCl. The common cations in Group I are:
- Ag⁺ forms AgCl (insoluble)
- Pb²⁺ forms PbCl₂ (insoluble)
- Hg₂²⁺ forms Hg₂Cl₂ (insoluble)

3. **Analyze Each Cation**:
- **Ag⁺**: When treated with dilute HCl, it forms AgCl, which is insoluble. Therefore, Ag⁺ belongs to Group I.
- **Pb²⁺**: When treated with dilute HCl, it forms PbCl₂, which is also insoluble. Therefore, Pb²⁺ belongs to Group I.
- **Hg₂²⁺**: When treated with dilute HCl, it forms Hg₂Cl₂, which is insoluble. Therefore, Hg₂²⁺ belongs to Group I.
- **Cd²⁺**: When treated with dilute HCl, cadmium does not form an insoluble chloride. Instead, it reacts with H₂S to form cadmium sulfide (CdS), which is an insoluble compound. Therefore, Cd²⁺ does not belong to Group I.

4. **Conclusion**: The cation that does not belong to Group I is **Cd²⁺ (Cadmium ion)**.

### Final Answer:
The cation that does not belong to Group I is **Cd²⁺ (Cadmium ion)**.

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