`HgS darr+Na_(2)S hArrNa_(2)[HgS_(2)]`

Options

A. For precipitate formation reaction
B. For precipitate dissolution reaction
C. For precipitate exchange reaction
D. For no reaction

Answer

To solve the given question regarding the reaction between mercury sulfide (HgS) and sodium sulfide (Na₂S) to form sodium dimercuric sulfide (Na₂[HgS₂]), we will analyze the reaction step by step.

### Step-by-Step Solution:

1. **Identify the Reactants and Products**:
- The reactants are mercury sulfide (HgS) and sodium sulfide (Na₂S).
- The product formed is sodium dimercuric sulfide (Na₂[HgS₂]).

2. **Understand the Nature of the Reactants**:
- HgS is known to be a precipitate, which means it is an insoluble compound that can form a solid in a solution.
- Na₂S is soluble in water, meaning it will dissociate into sodium ions (Na⁺) and sulfide ions (S²⁻).

3. **Analyze the Reaction**:
- When HgS reacts with Na₂S, the sulfide ions from Na₂S interact with the precipitate HgS.
- This interaction leads to the formation of a new compound, Na₂[HgS₂], which is also a precipitate.

4. **Determine the Type of Reaction**:
- Since HgS (the precipitate) is involved in the reaction and it is transformed into another compound (Na₂[HgS₂]), we need to classify the type of reaction.
- In this case, the original precipitate (HgS) is effectively dissolved during the reaction to form the new product.

5. **Conclusion**:
- The reaction can be classified as a **precipitate dissolution reaction** because the precipitate (HgS) is dissolved to form the product (Na₂[HgS₂]).

### Final Answer:
The correct classification of the reaction is **precipitate dissolution reaction**.

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