Final answer:
The incorrectly matched electrolyte is HCN/weak base, as HCN is a weak acid rather than a weak base, and the CN- anion from KCN makes the solution basic upon dissolution in water.
Step-by-step explanation:
Among the electrolytes listed, the one that is not correctly matched is HCN/weak base. Hydrogen cyanide (HCN) is actually a weak acid, not a weak base. When potassium cyanide (KCN) is dissolved in water, the CN- anion can react with water to form a weak acid (HCN) and OH- ions, which makes the solution basic, not acidic.
For the other options:
- KClO₃/soluble salt is correct; potassium chlorate is a soluble salt that comes from a strong base and a strong acid.
- Ba(OH)₂/strong soluble base is correct; barium hydroxide is a strong base and highly soluble.
- HNO₃/ strong acid is correct; nitric acid is a well-known strong acid.
- (NH₄)₂SO₄/soluble salt is correct; ammonium sulfate is a soluble salt that dissociates completely in water.