Halogens have an outer configuration of ns²p⁵ which shows it can accept one electron and are close to completing its octate; halogens show strong affinity to attract one electron and thushaving a higher electronegativity and show negative inductive effect.

Despite this the lone pairs present in halogens activate the benzene by positive resonance effect as shown above. The negative charge is developed at ortho and para positions thus activating it for electrophilic attack. Thus the net result of inductive and resonance effect is ortho-para directing nature of halogens.