It is known that the reaction of halobenzenes with potassium starch (KNH2) in liquid ammonia generating aniline occurs by an elimination-addition mechanism, with the formation of an intermediate capable of reacting with dienes to form Diels-Alder products.

a) Formulate the SNAr mechanism for non-activated aromatic compounds, highlighting crucial reaction intermediates.

b) Keeping in mind the halogen electronegativity order (F> Cl> Br> I) and the halide exit facility as the starting group (I> Br> Cl> F), explain the order of reactivity Br> I> Cl >> F against SNAr by elimination-addition, based on the mechanism proposed in the previous item.