Thermal decomposition releases carbon dioxide from magnesium carbonate

Steps:

• Identify the compounds in the mixture: magnesium carbonate (MgCO3) and magnesium nitrate (Mg(NO3)2).
• Heat causes MgCO3 to decompose into MgO and CO2 gas.
• Mg(NO3)2 decomposes into MgO, but the key gas identified in such experiments is CO2 from the carbonate.
• Strong heating in a hard-glass test-tube ensures complete decomposition without tube breakage.

Why A is correct:

• Magnesium carbonate decomposes as MgCO3(s) → MgO(s) + CO2(g), releasing carbon dioxide gas per standard thermal decomposition of carbonates.

Why the others are wrong:

• B. Magnesium nitrate decomposition produces nitrogen dioxide and oxygen, but the question focuses on CO2 from the carbonate component.
• C. Oxygen is a byproduct of nitrate decomposition, not the primary gas from the mixture.
• D. Incomplete option; does not match the formed gas.

Final answer: A