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

The reagent(s) used for softening the temporary hardness of water is (are)

The total number of cyclic isomers possible for a hydrocarbon with the molecular formula C₄H₆ is