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deduce / explain
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Oxygen has two common isotopes, 168O and 188O. (a) State the numbers of protons, neutrons and electrons in an atom of each. (b) An oxide ion has a charge of 2−. Write the symbol of the oxide ion formed from oxygen-18, with its mass number, proton number and charge. (c) (Supplement) Water made with oxygen-18 is called heavy-oxygen water. Explain why it gives the same result as ordinary water in the anhydrous copper(II) sulfate test, but has a greater mass for the same volume.
deduce: reach a conclusion from the information given. explain: give reasons and connect them to evidence.
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Scope and sources
Cambridge IGCSE Chemistry 0620 · 2026–2028 v2 · Original learning materials.
Isotopes (2.3 Core 1–2, Supplement 3–4): isotopes as atoms of the same element with the same number of protons and different numbers of neutrons, symbols for atoms and ions such as ¹²₆C and ³⁵₁₇Cl⁻, why isotopes have the same chemical properties (the same number of electrons and the same electronic configuration), and how to calculate relative atomic mass from isotope masses and abundances. Relative atomic mass measured against carbon-12, relative molecular mass, radioactivity and mass spectrometry are left to other modules or are not in the course.
Apparatus, amounts and times in the experiment are illustrative. Real practical work follows a teacher-approved safety method.
Official Cambridge syllabus