Science (086) — AI-generated practice question

The equation Mg + O₂ → MgO is only a skeletal chemical equation. It is unbalanced because the number of atoms of each element is not equal on both sides — there are 2 oxygen atoms on the LHS but only 1 on the RHS. According to the law of conservation of mass, a complete chemical equation must be balanced, with equal numbers of each type of atom on both sides.

The balanced equation is: 2Mg + O₂ → 2MgO

Source: Chapter 1, Section 1.1.1 and 1.1.2

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Examiners award marks for two key points:

1. Identifying it as a skeletal (unbalanced) equation and stating why it is unbalanced (atom count mismatch).
2. Linking to the law of conservation of mass — this is the scientific reason a balanced equation is required.

Writing the correct balanced equation earns the second mark. Do not just say "it needs balancing" — show the atom counts or state the law explicitly.