The correct order of increasing basicity of the given conjugate bases R=CH3 is

In carboxylate ion, the negative charge is present on oxygen, a most electronegative element here, thus it is resonance stabilized. HC≡C-: Carbon is sp hybridized so its electronegativity is increased higher relative to nitrogen. N¯H2 : Nitrogen is more electronegative than sp3 hybridized C-atom. From the above discussion, it is clear that the order of the stability of conjugated bases is as RCOO-