Which of the following pairs undergoes coupling reaction to form an Azo compound?

In $C_6{H}_{5}OC{H}_3, -OC{H}_3$ does not sufficiently increase electron density on the ring. Recall that $C_6{H}_{5}OH$  undergoes coupling in weakly alkaline medium which converts $C_6{H}_{5}OH$ to the more reactive $C_6{H}_{5}O$ –. In options (b) and (c), presence of electron-withdrawing —  $N{O}_2$ groups increases electrophilic character to such an extent that these diazonium cations can couple even with the compounds having weak electron-releasing groups. Option (d) undergoes coupling reaction easily because –  $NM{e}_2$ is sufficiently electron-releasing.