Assertion: `CdS` and `As_(2)S_(3)` are yellow coloured compounds.
Reason: CdS and `As_(2)S_(3)` can be separated by ammonium sulphide.

Options

A. If assertion is true but the reason is false
B. If assertion is false but reason is true
C. If both assertion and reason are true and reason is the correct explanation of assertion
D. If both assertion and reason are true but reason is not the correct explanation of assertion

Answer

To analyze the assertion and reason provided in the question, we will break down the information step by step.

### Step 1: Understand the Assertion
**Assertion:** CdS (Cadmium Sulfide) and As2S3 (Arsenic Trisulfide) are yellow-colored compounds.

- **Explanation:** Both CdS and As2S3 exhibit a yellow color due to their electronic structure. The yellow color arises from the absorption of light, which promotes electrons from the valence band to the conduction band. This phenomenon is a result of the specific energy levels present in these compounds.

### Step 2: Understand the Reason
**Reason:** CdS and As2S3 can be separated by ammonium sulfide.

- **Explanation:** When ammonium sulfide (NH4)2S is added to a mixture containing these two compounds, the solubility of each compound in ammonium sulfide differs.
- CdS is insoluble in ammonium sulfide, meaning it does not react or dissolve when ammonium sulfide is introduced.
- As2S3, on the other hand, reacts with ammonium sulfide to form a soluble thiosalt, which allows it to dissolve in the solution.

### Step 3: Conclusion on Assertion and Reason
- Both the assertion and the reason are true:
- **Assertion is true:** CdS and As2S3 are indeed yellow-colored compounds.
- **Reason is true:** They can be separated by ammonium sulfide due to their differing solubility.

### Step 4: Evaluate the Relationship
- However, while both statements are true, the reason provided does not explain why CdS and As2S3 are yellow. The yellow color is due to light absorption, not due to their solubility properties in ammonium sulfide.

### Final Answer
Thus, the correct conclusion is:
- **Option D:** Both assertion and reason are true, but the reason is not the correct explanation of the assertion.

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