Copper sub-group ppt. and arsenic salt -group ppt. are sepeated using (a) ____.

Answer

To solve the question regarding the separation of copper sub-group precipitate and arsenic salt-group precipitate, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Groups:**
- The copper sub-group precipitate is also known as Group 2A sulfides. This includes compounds like copper sulfide (CuS), cadmium sulfide (CdS), mercury sulfide (HgS), bismuth sulfide (Bi2S3), and lead sulfide (PbS).
- The arsenic sub-group precipitate is known as Group 2B sulfides, which includes arsenic sulfide (As2S3), antimony sulfide (Sb2S3), and tin sulfide (SnS).

2. **Understand the Solubility:**
- The key difference between these two groups is their solubility in yellow ammonium sulfide (YAS). The sulfides of Group 2A (copper sub-group) are insoluble in yellow ammonium sulfide, while the sulfides of Group 2B (arsenic sub-group) are soluble in yellow ammonium sulfide.

3. **Choose the Reagent for Separation:**
- Given the solubility characteristics, yellow ammonium sulfide can be used to separate the two groups. When yellow ammonium sulfide is added, the Group 2B sulfides will dissolve, while the Group 2A sulfides will remain as precipitates.

4. **Alternative Method:**
- Sodium hydroxide (NaOH) can also be used for the separation of these groups. The copper sub-group precipitates remain insoluble in NaOH, while the arsenic sub-group may react differently, allowing for further separation.

5. **Conclusion:**
- Therefore, the correct answer to the question is that copper sub-group precipitate and arsenic salt-group precipitate are separated using **yellow ammonium sulfide (YAS)** or **sodium hydroxide (NaOH)**.

### Final Answer:
Copper sub-group ppt. and arsenic salt-group ppt. are separated using **yellow ammonium sulfide (YAS)** or **sodium hydroxide (NaOH)**.

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