Q.Some meta-directing substituents in aromatic substitution are given. Which one is most deactivating?

Directing Effects of Substituents

Once a substituent is already on a benzene ring, a second electrophilic substitution is controlled by that first group along TWO independent axes: whether it speeds up (ACTIVATING) or slows down (DEACTIVATING) the reaction relative to plain benzene, and whether it directs the new electrophile to the ORTHO/PARA positions or to the META position.

Ortho-para directors raise electron density specifically at the ortho and para ring positions. Every ACTIVATING group (-OH, -NH2, -NHR, -NHCOCH3, -OCH3, -CH3, -C2H5, etc.) is an ortho-para director: a lone pair on the atom attached to the ring (e.g. phenol's -OH oxygen) delocalises into the ring by resonance, and the resonance structures that result place the extra electron density specifically at ortho/para -- so the ring is BOTH more electron-rich overall (activated) AND selectively more nucleophilic at ortho/para. Aryl HALOGENS are the one notable exception to the activating-equals-ortho-para-directing pattern: a halogen's strong inductive electron-withdrawal makes the ring LESS electron-rich overall (deactivating, so halobenzenes react more slowly than benzene), yet the halogen's lone pair can still donate into the ring by resonance at ortho/para specifically -- so halogens are DEACTIVATING but still ORTHO-PARA DIRECTING, a combination unique to this group among common substituents. …