Lead has been placed in qualitative group analysis 1st and 2nd because

Options

A. It shown the valency one and two
B. it forms insoluble `PbCl_(2)`
C. It form lead salphide
D. `PbCl_(2)` is parially soluble in water

Explanation

### Step-by-Step Solution:

1. **Understanding the Qualitative Group Analysis**:
- Qualitative analysis groups cations based on their solubility and the type of precipitates they form when treated with specific reagents.

2. **Lead's Valency**:
- Lead (Pb) exhibits two common oxidation states: +1 and +2. This property allows it to form different compounds that can behave differently in qualitative analysis.

3. **Formation of Lead Chloride**:
- Lead forms lead(II) chloride (PbCl2), which is slightly soluble in water. This property is crucial because it means that not all lead ions can be precipitated out of solution when dilute hydrochloric acid (HCl) is added.

4. **Behavior in Group Analysis**:
- In the first group of qualitative analysis, lead ions are partially precipitated as lead chloride when HCl is added. However, because PbCl2 is only slightly soluble, some lead remains in solution.

5. **Formation of Lead Sulfide**:
- In the second group, lead can also form lead sulfide (PbS) when treated with hydrogen sulfide (H2S) in an acidic medium. This is another important aspect of its classification.

6. **Conclusion**:
- Therefore, lead is placed in both the first and second qualitative groups due to its ability to form lead chloride (which is partially soluble) and lead sulfide (which is insoluble). This dual behavior is why lead is classified in both groups.

### Final Answer:
Lead has been placed in qualitative group analysis 1st and 2nd because it forms lead chloride (PbCl2), which is slightly soluble in water, and lead sulfide (PbS), which is insoluble. This dual behavior allows lead to be classified in both groups.

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