The species which by definition has ZERO standard molar enthalpy of formation at 298 K is

Among the following, the intensive property is (properties are)

Aqueous solution of HNO₃, KOH and CH₃COOH and CH₃COONa of identical concentrations are provided. The pairs of solutions which form a buffer upon mixing is(are)

Amongst the following the total number of compounds whose aqueous solution turns red litmus paper blue is
KCN, K₂SO₄, (NH₄)₂C₂O₄, NaCl, Zn(NO₃)₂, FeCl₃, K₂CO₃, NH₄NO₃ and LiCN