Which of the following compound() during heating undergo redox decomposition reaction?

Options

A. `HgCO_(3)(s)`
B. `Ag_(2)C_(2)O_(4)(s)`
C. `FeCl_(3)*6H_(2)O(s)`
D. `K_(2)Cr_(2)O_(7)(s)`

Explanation

To determine which of the given compounds undergo a redox decomposition reaction upon heating, we will analyze each compound one by one, focusing on the changes in oxidation states of the elements involved.

### Step-by-Step Solution:

1. **Analyze HgCO3 (Mercury(II) Carbonate)**:
- Upon heating, HgCO3 decomposes into Hg (mercury) and CO2 (carbon dioxide).
- The reaction can be represented as:
\[ \text{HgCO}_3 \rightarrow \text{Hg} + \text{CO}_2 \]
- In this reaction, the oxidation state of Hg changes from +2 (in HgCO3) to 0 (in Hg). This indicates a reduction process.
- Therefore, HgCO3 undergoes a redox reaction.

2. **Analyze Ag2C2O4 (Silver(II) Oxalate)**:
- When heated, Ag2C2O4 decomposes into Ag (silver) and CO2 (carbon dioxide):
\[ \text{Ag}_2\text{C}_2\text{O}_4 \rightarrow 2\text{Ag} + 2\text{CO}_2 \]
- The oxidation state of Ag changes from +1 (in Ag2C2O4) to 0 (in Ag). This indicates a reduction process.
- Therefore, Ag2C2O4 also undergoes a redox reaction.

3. **Analyze FeCl3.6H2O (Iron(III) Chloride Hexahydrate)**:
- Upon heating, FeCl3.6H2O decomposes to form Fe2O3 (iron(III) oxide), HCl (hydrochloric acid), and water:
\[ 2\text{FeCl}_3 \cdot 6\text{H}_2\text{O} \rightarrow \text{Fe}_2\text{O}_3 + 6\text{HCl} + 9\text{H}_2\text{O} \]
- The oxidation state of Fe remains +3 in both reactants and products, indicating no change in oxidation state.
- Therefore, this is not a redox reaction.

4. **Analyze K2Cr2O7 (Potassium Dichromate)**:
- When heated, K2Cr2O7 decomposes to form K2CrO4 (potassium chromate) and Cr2O3 (chromium(III) oxide):
\[ \text{K}_2\text{Cr}_2\text{O}_7 \rightarrow \text{K}_2\text{CrO}_4 + \text{Cr}_2\text{O}_3 \]
- The oxidation state of Cr changes from +6 (in K2Cr2O7) to +3 (in Cr2O3), indicating a reduction process.
- Therefore, K2Cr2O7 undergoes a redox reaction.

### Conclusion:
From the analysis:
- **HgCO3**: Redox reaction
- **Ag2C2O4**: Redox reaction
- **FeCl3.6H2O**: Not a redox reaction
- **K2Cr2O7**: Redox reaction

Thus, the compounds that undergo redox decomposition reactions upon heating are **HgCO3, Ag2C2O4, and K2Cr2O7**.

### Final Answer:
The compounds that undergo redox decomposition reactions during heating are **HgCO3, Ag2C2O4, and K2Cr2O7**.

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