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2017 O Level Chem P1 Q27 — Periodic Table / Elements and Properties Solution

Periodic Table / Elements and Properties 2017 O Level Pure Chemistry · Paper 1 · Q27

Question

P, Q, R and S are elements in the Periodic Table. • Q and R are formed as elements at the positive electrode during electrolysis. • P and S both conduct electricity. • P has a higher melting point than S. • Q displaces R from aqueous solutions containing R⁻ ions. Which statement could be correct?

AP could be Na and S could be Li.
BQ could be Br₂ and R could be I₂.
CR would be paler in colour than Q.
DS exists as diatomic molecules.

Correct answer: B

Video Solution

Explanation

Answer: B. Q and R are discharged at the positive electrode, so they are non-metals (halogens), and Q displaces R, so Q is the more reactive halogen. Bromine displaces iodine from iodide solutions, so Q could be \(\text{Br}_2\) and R could be \(\text{I}_2\).

A is wrong (sodium has a lower melting point than lithium). C is wrong (iodine is darker than bromine, not paler). D is wrong (S is a metal that conducts, not a diatomic molecule).

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