When magnesium metal (Mg) burns in oxygen (O2), which oxide compound is formed as the principal product of this combustion reaction?

Introduction / Context:
The burning of magnesium ribbon in air is a classic school experiment that demonstrates combustion and oxidation of metals. When magnesium burns, it combines with oxygen to form a white powdery oxide. This question asks for the correct formula of that oxide, reinforcing understanding of valency rules, formula writing, and basic redox chemistry.

Given Data / Assumptions:

• Reactants: magnesium metal (Mg) and oxygen gas (O2).
• The reaction is a combustion or oxidation reaction.
• We are asked for the correct empirical formula of the oxide product.
• Magnesium is a Group 2 metal with valency 2.

Concept / Approach:
Magnesium forms a simple ionic oxide in which magnesium has an oxidation state of +2 and oxygen has an oxidation state of -2. To balance charges, one Mg2+ ion combines with one O2- ion, giving the formula MgO. The balanced chemical equation for the reaction is 2Mg + O2 gives 2MgO. Other formulas such as Mg2O or MgO4 are not consistent with the usual valencies of magnesium and oxygen in this context.

Step-by-Step Solution:

Verification / Alternative check:
In the laboratory, burning magnesium produces a bright white flame and leaves behind a white powder identified as magnesium oxide. Chemical analysis and textbooks consistently give the formula of this oxide as MgO. If we tried other formulas, such as Mg2O, the charges would not balance properly for the simple oxide. MgO also fits with trends among Group 2 metals, which typically form MO type oxides, such as CaO and BaO. This pattern supports MgO as the correct formula for the product.

Why Other Options Are Wrong:

• Mg2O: Implies a ratio that would not maintain simple charge neutrality with Mg2+ and O2- ions.
• MgO4: Suggests an unrealistic oxidation state for magnesium in a simple oxide and does not correspond to known magnesium compounds formed by simple combustion.
• O2Mg: This is just another way of writing MgO2 if misinterpreted and is not the standard formula for the common magnesium oxide product.
• Mg2O3: Does not correspond to the stable oxide formed during burning of magnesium in air.

Common Pitfalls:
Students sometimes misinterpret the stoichiometric coefficients in the balanced equation as subscripts in the formula. For example, seeing 2Mg + O2 gives 2MgO might lead some to think the compound is Mg2O, which is not correct. To avoid this, always derive the formula from charge balance and valency, not from equation coefficients. Another error is to overcomplicate the formula by adding extra oxygen atoms that are not required for charge neutrality.

Final Answer:
When magnesium burns in oxygen, the main product formed is MgO, magnesium oxide.