Revision method

For Physics, test whether each formula uses the requested physical quantity and SI unit. For Chemistry, balance atoms and charge before deciding a reaction or compound. For Biology, follow the structure and process named in the question, and avoid turning a textbook trend into an absolute statement. Mixed practice should combine all three subjects.

Source and rights note

The lessons, explanations and diagrams are original study material developed for this edition. External reference sources supplied facts and terminology only; no textbook exercises, figures or page layouts were copied. The local source register records factual cross-checks and editorial limitations.