Let's balance the given chemical reactions step-by-step.

### Reaction 1: MgCO3 + HCl
The reaction between magnesium carbonate (MgCO3) and hydrochloric acid (HCl) produces magnesium chloride (MgCl2), carbon dioxide (CO2), and water (H2O). The balanced equation is:

\[ \text{MgCO}_3 + 2 \text{HCl} \rightarrow \text{MgCl}_2 + \text{CO}_2 + \text{H}_2\text{O} \]

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### Reaction 2: CaCO3 + H2SO4
The reaction between calcium carbonate (CaCO3) and sulfuric acid (H2SO4) produces calcium sulfate (CaSO4), carbon dioxide (CO2), and water (H2O). The balanced equation is:

\[ \text{CaCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CaSO}_4 + \text{CO}_2 + \text{H}_2\text{O} \]

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### Reaction 3: MgSO3 + HCl
The reaction between magnesium sulfite (MgSO3) and hydrochloric acid (HCl) produces magnesium chloride (MgCl2), sulfur dioxide (SO2), and water (H2O). The balanced equation is:

\[ \text{MgSO}_3 + 2 \text{HCl} \rightarrow \text{MgCl}_2 + \text{SO}_2 + \text{H}_2\text{O} \]

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### Reaction 4: Na2SO3 + H2SO4
The reaction between sodium sulfite (Na2SO3) and sulfuric acid (H2SO4) produces sodium sulfate (Na2SO4), sulfur dioxide (SO2), and water (H2O). The balanced equation is:

\[ \text{Na}_2\text{SO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + \text{SO}_2 + \text{H}_2\text{O} \]

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In summary, the balanced products for the reactions are:

1. **MgCO3 + HCl** → MgCl2 + CO2 + H2O
2. **CaCO3 + H2SO4** → CaSO4 + CO2 + H2O
3. **MgSO3 + HCl** → MgCl2 + SO2 + H2O
4. **Na2SO3 + H2SO4** → Na2SO4 + SO2 + H2O