Which (------COOH) group is easaily decarboxylated on heating and why?

Explanation

The (------COOH) group which is attached to the following groups is easily lost, `beta`-ketop, `beta`-cyano, and `beta`-unsaturated C atom. Out of the two (-----COOH) group attached to the same C atom, one (-----COOH) is easily lost as -----`CO_(2)` on heating, due to NGP (neighbouring group particiation). If the (----COOH) group is attached to any of the above ground and EWG (electron-withdrawing group) is also present on `gamma`-C atom, then the compound is stable and does not lose `CO_(2)`.
i.
ii.
iii.
Stable on heating and dose not lose `CO_(2)`, due to three EWG F atoms.