More stronger be the acid, more chances to give up the proton (H+) by an acid and becomes carboxylate ion. The process of releasing the proton and to become a carboxylate ion is known as decarboxylate process. If electron withdrawing groups (such as −NO2, −Cl etc ) are attached to the benzene ring at ortho and para positions, they will increase the acidic strength of the acid means, it will release the protons easily. So, 2,4,6 -trinitrobenzoic acid will decarboxylate easily. Thus, (c) is the correct option.