Science (086) — AI-generated practice question

Changing subscripts in a chemical formula changes the identity of the substance itself. For example, writing H₂O₄ instead of H₂O gives a completely different compound. According to the law of conservation of mass, the number of atoms of each element must remain equal on both sides. To achieve this balance, we can only change coefficients (number of molecules), never subscripts.

Source: Chapter 1, Section 1.1.2 — Balanced Chemical Equations

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Examiners look for two key points (1 mark each):

1. Changing subscripts changes the chemical formula/identity of the substance.
2. Only coefficients may be changed to balance an equation (to satisfy the law of conservation of mass).

Avoid saying "it breaks the rules" — always link it to the law of conservation of mass and the identity of the compound. Keep the example brief but precise.