The figure below shows four different substituted aryl halides labeled P, Q, R, and S. These compounds undergo nucleophilic aromatic substitution when heated with aqueous NaOH. The reaction proceeds via an addition-elimination mechanism involving a carbanion intermediate. Identify the correct decreasing order of reactivity for these compounds towards this reaction.

Step-by-step solution

Nucleophilic aromatic substitution ( S_ N Ar ) proceeds via an addition-elimination mechanism, forming a carbanion intermediate (Meisenheimer complex) in the rate-determining step. The reactivity of aryl halides towards S_ N Ar increases with the presence of electron-withdrawing groups (EWGs) at the ortho and para positions, as they stabilize the carbanion intermediate through -I and -M effects. Conversely, electron-donating groups (EDGs) destabilize the intermediate and decrease reactivity. Analyzing the given com