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2021 O Level Chem P1 Q21 — Atomic Structure / Atoms and Ions Solution

Atomic Structure / Atoms and Ions 2021 O Level Pure Chemistry · Paper 1 · Q21

Question

The table shows data for atoms or ions of the elements P, Q, R and S. The letters do not represent the chemical symbols of the elements. Which statement is correct? Question diagram

Question diagram

AP and Q are non-metallic.
BP and R react to form an ionic compound.
CQ and S are unreactive.
DR and S would be in the same group of the Periodic Table.

Correct answer: B

Video Solution

Explanation

Answer: B. Use the proton number to identify the element, and compare electrons with protons to decide atom or ion. P: 11 protons (sodium), 10 electrons → Na⁺. Q: 13 protons (aluminium), 13 electrons → a neutral Al atom. R: 17 protons (chlorine), 18 electrons → Cl⁻. S: 18 protons (argon), 18 electrons → a neutral Ar atom.

Option B is correct: P (Na⁺) and R (Cl⁻) are already a cation and an anion, and they combine to form the ionic compound sodium chloride, NaCl.

A is wrong (sodium and aluminium are metals); C is wrong (aluminium is reactive); D is wrong (chlorine is in Group VII while argon is in Group 0).

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