Why Benzaldehyde is metadirecting for nucleophilic substitution rections ?

Explanation

Aldehydic group (-CHO) is meta-directing in nature for electrophilic substitution reaction in benzene ring because this group is electron withdrawing in nature, i.e., having - I effect. Due to this effect, it decreases the electron density on the ortho and para positions as compared to meta position. It can be seen in the following resonating structures.

Positive charge on ortho and para positions has no attraction for incoming electrophile. While meta position attracts the electrophile or we can say that electrophilic substitution takes place at meta position in aromatic aldehydes.