Question

Identify the correct order of solubility in aqueous medium :

• A. ${ Na2S > ZnS > CuS }$
• B. ${ CuS > ZnS > Na2S }$
• C. ${ZnS > Na2S > CuS }$
• D. ${Na2S < CuS > ZnS}$

Answer 1

Answer: (A)

${ Na2S > ZnS > CuS }$

Answer 2

Ionic compounds are more soluble in water or in aqueous medium.
According to Fajans' rule,
Size of the cation increases the ionic character also increases.
Ionic character oc size of cation (if anion is same)
The order of size of cation is
$Na^+ > Zn^{2+} > Cu^{2+}$
$\therefore \, \, \,$The order of ionic character and hence, of solubility in water is as
$Na_2S > ZnS > CuS$