Final answer:
Among the given options, (b) KNO₃ and K₂SO₄ is the pair where both members are salts.
Step-by-step explanation:
In the given pairs of substances, the one where both members are salts is (b) KNO₃ and K₂SO₄. Salts are compounds formed by the neutralization reaction of an acid and a base and consist of a cation other than H+ and an anion other than OH-. Both potassium nitrate (KNO₃) and potassium sulfate (K₂SO₄) meet these criteria as they are ionic compounds consisting of potassium cations (K+) and either nitrate (NO3-) or sulfate (SO42-) anions, which are typical components of salts.
(a) NaCl and NaOH does not qualify because NaOH is a strong base, not a salt. (c) H₃PO₄ and (NH₄)₃PO₄ also do not qualify because H₃PO₄ is an acid, whereas (NH₄)₃PO₄ is a salt formed by the neutralization of phosphoric acid with ammonium hydroxide.