stable oxide is obtained by heating the carbonate of the elements

Options

A. Li
B. Na
C. K
D. Rb

Explanation

To solve the question of which alkali metal carbonate forms a stable oxide upon heating, we can follow these steps:

### Step 1: Identify the Alkali Metals
The alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs).

### Step 2: Understand the General Formula of Alkali Metal Carbonates
The general formula for alkali metal carbonates is M2CO3, where M represents the alkali metal.

### Step 3: Analyze the Stability of Carbonates
Among the alkali metal carbonates, lithium carbonate (Li2CO3) is known to be less stable compared to the carbonates of other alkali metals.

### Step 4: Heating of Carbonates
When heated, lithium carbonate decomposes readily to form lithium oxide (Li2O) and carbon dioxide (CO2):
\[ \text{Li}_2\text{CO}_3 \rightarrow \text{Li}_2\text{O} + \text{CO}_2 \]

### Step 5: Compare with Other Alkali Metal Carbonates
The carbonates of sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs) are more stable and do not decompose upon heating. This is due to their larger cation sizes, which result in lower lattice energy compared to lithium.

### Step 6: Understand the Reason for Lithium's Decomposition
The small size of the lithium ion (Li+) leads to a higher lattice energy and stronger polarization of the carbonate bond, weakening the CO bond and allowing for decomposition.

### Conclusion
Thus, the stable oxide obtained by heating the carbonate of the alkali metals is primarily from lithium carbonate, which decomposes to form lithium oxide.

### Summary
The answer to the question is that the stable oxide is obtained from heating lithium carbonate (Li2CO3), which decomposes to form lithium oxide (Li2O) and carbon dioxide (CO2).

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