Answer: A (aqueous potassium hydroxide and dilute hydrochloric acid). Potassium chloride is soluble, so it cannot be made by precipitation, and potassium is too reactive to add to acid safely.
The standard method for a soluble salt of a Group 1 metal is titration of the alkali with the acid: \(\text{KOH} + \text{HCl} \rightarrow \text{KCl} + \text{H}_2\text{O}\). This is controlled and gives a pure product after crystallisation.
B leaves a mixture of ions with no way to isolate pure KCl. C (potassium and chlorine) and D (potassium and acid) both react dangerously. Answer A.
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