Q.Which of the following is a strong electrolyte ? HF, AgCl, $\mathrm{CuSO_4}$, $\mathrm{CH_3COONH_4}$, $\mathrm{H_3PO_4}$.

Step 1. The question tests whether 'strong electrolyte' is being confused with 'highly soluble' or 'gives a neutral solution' -- neither is the correct criterion.

Step 2. Being a strong electrolyte means: whatever amount of the substance DOES dissolve, dissociates almost completely into ions. It says nothing about how MUCH dissolves (solubility) or about whether those ions later react further with water (hydrolysis).

Step 3. AgCl is only sparingly soluble, but the small amount that dissolves is 100% ionized as Ag+ and Cl- -- so AgCl is a strong electrolyte. CuSO4 is a soluble salt, fully ionized -- strong electrolyte. CH3COONH4 is a salt of a weak acid and a weak base, but the salt ITSELF still dissociates essentially completely into CH3COO- and NH4+ on dissolving (those ions may go on to hydrolyse with water, a separate phenomenon from section 3.7, but the initial dissociation of the salt is still complete) -- so it too is a strong electrolyte …

Classify each substance as a salt (strong electrolyte by default) or a weak acid/base (weak electrolyte), ignoring sol …

• Calling AgCl a weak electrolyte because it is only sparingly soluble -- solubility and degree of ionization are different properties. …