Question

Why halogens are electron withdrawing and ring deactivating but ortho para directing groups

Answer 1

Halogens bonded to benzene ring has three lone pairs. These three electron pairs can cause resonance in benzene ring. But, halogens are also highly electronegative and thus they have strong -I effect.

Answer 2

Since halogens have -I effect, hence they are deactivating.

Also, their +R effect accounts for their ortho-para directing activity.