Which of the following alkali metal carbonate is the least stable and decomposes readily

Options

A. `Li_(2)CO_(3)`
B. `Na_(2)CO_(3)`
C. `K_(2)CO_(3)`
D. `Cs_(2)CO_(3)`

Answer

To determine which alkali metal carbonate is the least stable and decomposes readily, we can analyze the stability of the carbonates based on the size and charge of the metal ions involved. Here’s a step-by-step solution:

### Step 1: Identify the Alkali Metal Carbonates
The given alkali metal carbonates are:
- Li2CO3 (Lithium Carbonate)
- Na2CO3 (Sodium Carbonate)
- K2CO3 (Potassium Carbonate)
- Cs2CO3 (Cesium Carbonate)

### Step 2: Understand Thermal Stability
Thermal stability of metal carbonates generally depends on two main factors:
1. **Size of the Metal Ion**: Smaller metal ions tend to form stronger bonds with the carbonate ion, leading to greater stability.
2. **Charge of the Metal Ion**: Higher charge on the metal ion can also contribute to increased stability.

### Step 3: Analyze the Size of the Ions
In the alkali metals, the size of the ions increases as we move down the group from Lithium (Li) to Cesium (Cs):
- Li+ < Na+ < K+ < Cs+

### Step 4: Analyze the Charge of the Ions
All the alkali metals in this context have a +1 charge (Li+, Na+, K+, Cs+). Therefore, the charge factor does not differentiate their stability.

### Step 5: Determine Stability Trend
Based on the size of the ions:
- As we move from Li2CO3 to Cs2CO3, the size of the metal ion increases, which generally leads to a decrease in thermal stability. Thus, the stability trend is:
- Li2CO3 < Na2CO3 < K2CO3 < Cs2CO3

### Step 6: Conclusion
Since Li2CO3 has the smallest metal ion (Li+) among the given options, it is the least stable and decomposes readily compared to the other carbonates.

### Final Answer
The least stable alkali metal carbonate that decomposes readily is **Li2CO3**.

---