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2025 O Level Chem P1 Q18 — Salts / Solubility Solution

Salts / Solubility 2025 O Level Pure Chemistry · Paper 1 · Q18

Question

Which solid is insoluble in water?

AMg(OH)₂
BNa₂CO₃
CCuSO₄
DPb(NO₃)₂

Correct answer: A

Video Solution

Explanation

Answer: A. Apply the standard solubility rules:

All sodium salts are soluble → \(\text{Na}_2\text{CO}_3\) is soluble (B out).
Most sulfates are soluble, including \(\text{CuSO}_4\) (C out).
All nitrates are soluble → \(\text{Pb(NO}_3)_2\) is soluble (D out).
Most hydroxides are insoluble (only Group I hydroxides + \(\text{NH}_4\text{OH}\) are soluble), so \(\text{Mg(OH)}_2\) is insoluble.

Answer A.

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