Science (086) — AI-generated practice question

No, $\text{Mg} + \text{O}_2 \rightarrow \text{MgO}$ is not a balanced chemical equation.

Reason: The number of atoms of each element is not equal on both sides. There are 2 oxygen atoms on the LHS but only 1 oxygen atom on the RHS. Hence, the mass is not conserved.

Law: A balanced chemical equation must satisfy the Law of Conservation of Mass, which states that mass can neither be created nor destroyed in a chemical reaction, so the total mass of reactants equals the total mass of products.

The balanced equation is: $2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$

Source: Chapter 1, Sections 1.1.1 and 1.1.2

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• 1 mark for stating it is NOT balanced.
• 1 mark for the reason — unequal number of oxygen atoms on LHS (2) and RHS (1). Examiners want you to count atoms specifically.
• 1 mark for naming the Law of Conservation of Mass (full name required).
• Writing the correctly balanced equation is a good add-on and shows understanding, but do not skip naming the law — that is the direct mark-fetch here.