The figure shows the variation of solubility of common ionic solids in water with temperature. According to the graph, the solubility of which substance **decreases** with rising temperature? 
AKNO₃
BNa₂SO₄
CNaNO₃
DKBr
Answer & Solution
Correct answer: B. Na₂SO₄
Na₂SO₄ shows the descending curve — its dissolution becomes net exothermic above a critical temperature, so heat shifts equilibrium backward. The other three (KNO₃, NaNO₃, KBr) show rising solubility with T.
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