Ionic species are stabilised by the dispersal of charge. When the carboxylate ion is attached to an electronegative atom the negative charge is dispersed on them due to dipole moment leading to stability of carboxylate ion. More the number of electronegative species attached more is the dipole moment and hence more dispersal leading to more stability. In the above case the 4th option has two ‘F’ attached while 3rd one has only one ‘F’ attached, 2nd option has ‘Cl’ attached out of F and Cl, F is more electronegative. The 1st option is simple carboxylate ion which is only resonance stabilized, there is no dipole moment there.
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