Nuclear charge is defined as the net positive charge experienced by an electron in the orbital of an atom exerted by the nucleus of the atom. The closer the orbital, the greater is the nuclear charge experienced by the electron [s] in it and the nuclear charge is inversely proportional to the distance of the electron from the nucleus.

Silicon has greater nuclear charge [+14] than aluminium [+13].

Hence the effective nuclear charge exerted on unpair 3p electron of silicon would be greater as compared to that of aluminium.