Which of the following oxide is least stable?

Options

A. `CO_2`
B. CO
C. MgO
D. HgO

Answer

To determine which oxide is the least stable among the given options, we will analyze the stability of each oxide based on the oxidation states of the elements involved.

### Step-by-Step Solution:

1. **Identify the Oxides**:
We need to analyze the stability of the following oxides:
- CO (Carbon monoxide)
- CO2 (Carbon dioxide)
- MgO (Magnesium oxide)
- HgO (Mercury(II) oxide)

2. **Analyze Carbon Oxides**:
- **CO (Carbon monoxide)**: Carbon in CO has an oxidation state of +2. It is relatively stable due to the strong bond between carbon and oxygen.
- **CO2 (Carbon dioxide)**: In CO2, carbon has an oxidation state of +4, which is the most stable oxidation state for carbon. Thus, CO2 is very stable.

3. **Analyze Magnesium Oxide**:
- **MgO (Magnesium oxide)**: Magnesium has an oxidation state of +2 in MgO, which is its most stable oxidation state. Therefore, MgO is also stable.

4. **Analyze Mercury Oxide**:
- **HgO (Mercury(II) oxide)**: Mercury can exist in multiple oxidation states, but its most stable oxidation state is +2. However, HgO is less stable compared to other oxides due to the tendency of mercury to exist in the +1 oxidation state (as in Hg2O).

5. **Conclusion**:
- Among the oxides analyzed, **HgO** is the least stable because mercury prefers to exist in the +1 oxidation state, making HgO less stable compared to the other oxides.

### Final Answer:
The least stable oxide among the options is **HgO (Mercury(II) oxide)**.

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