Which of the following oxide is thermaly least stable?

Options

A. CaO
B. `Al_2O_3`
C. `Fe_2O_3`
D. `Ag_2O`

Answer

To determine which of the following oxides is thermally least stable among Calcium Oxide (CaO), Aluminum Oxide (Al2O3), Iron(III) Oxide (Fe2O3), and Silver Oxide (Ag2O), we can analyze the thermal stability of each compound based on the nature of their bonding and the distribution of their valence electrons.

### Step-by-Step Solution:

1. **Understanding Thermal Stability**:
- Thermal stability refers to the ability of a compound to withstand high temperatures without decomposing. The stability of an oxide often depends on the nature of the metal, the type of bonding, and the arrangement of valence electrons.

2. **Analyzing Each Oxide**:
- **Calcium Oxide (CaO)**:
- Calcium is an alkaline earth metal, and its oxide is known to be reactive. CaO can react with water to form calcium hydroxide (Ca(OH)2), indicating that it is less stable at high temperatures.
- **Aluminum Oxide (Al2O3)**:
- Aluminum oxide is known for its high thermal stability due to the strong ionic and covalent character of its bonds. It does not decompose easily at elevated temperatures.
- **Iron(III) Oxide (Fe2O3)**:
- Iron(III) oxide is also relatively stable thermally. It can withstand high temperatures and does not readily decompose.
- **Silver Oxide (Ag2O)**:
- Silver oxide is less stable than the previous two oxides but is still more stable than calcium oxide. It can decompose upon heating to produce silver and oxygen.

3. **Comparing Stability**:
- Among the four oxides, Calcium Oxide (CaO) is the most reactive and least stable thermally because it readily reacts with water and can decompose at lower temperatures compared to the others.

4. **Conclusion**:
- Therefore, the oxide that is thermally least stable among the given options is **Calcium Oxide (CaO)**.

### Final Answer:
**Calcium Oxide (CaO)** is the thermally least stable oxide among the options provided.