Which of the following metal carbonates is decomposed on heating?

Options

A. `MgCO_3`
B. `Na_2CO_3`
C. `K_2CO_3`
D. `Pb_2CO_3`

Explanation

To determine which of the following metal carbonates decomposes on heating, we will analyze each of the given options: magnesium carbonate, sodium carbonate, potassium carbonate, and lead carbonate.

### Step-by-Step Solution:

1. **Identify the Carbonates**: The carbonates we need to consider are:
- Magnesium carbonate (MgCO₃)
- Sodium carbonate (Na₂CO₃)
- Potassium carbonate (K₂CO₃)
- Lead carbonate (PbCO₃)

2. **Understand Thermal Stability**:
- Alkali metal carbonates (like sodium and potassium carbonates) are generally stable when heated. They do not decompose easily.
- Alkaline earth metal carbonates (like magnesium carbonate) and some other metal carbonates (like lead carbonate) can decompose upon heating.

3. **Analyze Each Carbonate**:
- **Sodium Carbonate (Na₂CO₃)**: This carbonate is stable upon heating and does not decompose.
- **Potassium Carbonate (K₂CO₃)**: Similar to sodium carbonate, potassium carbonate is stable and does not decompose on heating.
- **Magnesium Carbonate (MgCO₃)**: This carbonate decomposes when heated, producing magnesium oxide (MgO) and carbon dioxide (CO₂).
\[ \text{MgCO}_3 \, \text{(s)} \xrightarrow{\text{heat}} \text{MgO} \, \text{(s)} + \text{CO}_2 \, \text{(g)} \]
- **Lead Carbonate (PbCO₃)**: Lead carbonate also decomposes on heating, yielding lead oxide (PbO) and carbon dioxide (CO₂).
\[ \text{PbCO}_3 \, \text{(s)} \xrightarrow{\text{heat}} \text{PbO} \, \text{(s)} + \text{CO}_2 \, \text{(g)} \]

4. **Conclusion**: From the analysis, we find that:
- Sodium carbonate and potassium carbonate do not decompose on heating.
- Magnesium carbonate and lead carbonate do decompose on heating.

Therefore, the metal carbonates that decompose on heating are **magnesium carbonate (MgCO₃)** and **lead carbonate (PbCO₃)**.