Which of the following alkaline earth metal carbonate is thermally
least stable?

Options

A. `BeCO_(3)`
B. `CaCO_(3)`
C. `MgCO_(3)`
D. `BaCO_(3)`

Explanation

To determine which alkaline earth metal carbonate is thermally least stable, we can follow these steps:

### Step 1: Understand the trend in thermal stability of alkaline earth metal carbonates
As we move down the group of alkaline earth metals (from Beryllium to Barium), the thermal stability of their carbonates increases. This is due to the increasing electropositive character of the metals.

**Hint:** Consider how the position of the metal in the periodic table affects its properties.

### Step 2: Analyze the factors affecting stability
The stability of alkaline earth metal carbonates is influenced by hydration energy and electropositive character. As we go down the group, the hydration energy decreases, leading to a decrease in solubility, which in turn increases thermal stability.

**Hint:** Think about how hydration energy relates to the solubility of the carbonates.

### Step 3: Identify the carbonates of alkaline earth metals
The carbonates we are considering include:
- Beryllium carbonate (BeCO3)
- Magnesium carbonate (MgCO3)
- Calcium carbonate (CaCO3)
- Strontium carbonate (SrCO3)
- Barium carbonate (BaCO3)

**Hint:** List the carbonates of the alkaline earth metals in order of their position in the periodic table.

### Step 4: Compare the thermal stability of the carbonates
Beryllium carbonate is known to be the least stable among these carbonates. It decomposes at a relatively low temperature (below 373 K), while the other carbonates require higher temperatures for decomposition.

**Hint:** Recall the decomposition temperatures of the carbonates to compare their stability.

### Step 5: Conclusion
Based on the above analysis, we conclude that the alkaline earth metal carbonate that is thermally least stable is Beryllium carbonate (BeCO3).

**Final Answer:** BeCO3 (Beryllium carbonate) is the least thermally stable alkaline earth metal carbonate.

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