Answer:
B. [tex]Na_2SO_4[/tex]
Explanation:
Hello,
The solubility of HgS is increased by adding [tex]Na_2SO_4[/tex] due to common ion effect which consists on the effect that the higher solubility of [tex]Na_2SO_4[/tex] has over the HgS as the sulfur-based ions modify the solubility product. In such a way, by adding the sulfate, the equilibrium will be shifted rightwards, therefore the solubility is increased.
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