Question
Identify the correct order of solubility in aqueous medium
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CuS> ZnS> Na2S
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ZnS > Na2S> CuS
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Na2S> CuS> ZnS
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Na2S> ZnS> CuS
Solution
D.
Na2S> ZnS> CuS
Ionic compounds are more soluble in water or in an aqueous medium.
Ionic character 
Size of cation (if cation is same)
The order os size of cation is
Na+> Zn2+>Cu2+
therefore,
The order of ionic character and hence, of solubility in water is as
Na2S > ZnS> CuS
