Question regarding -I (negative inductive effect) producing group - Organic chemistry

sankalpmittal

Why is Nitrogen dioxide , a strong -I producing group that fluorine , or chlorine etc ? This must mean that NO₂ is more electronegative that halogens also , but why is it so ? Is it due to resonance ? Or due to the fact that its formed from a coordinate compound HNO₃ ?

I wondered for this question long , but failed to obtain answer...

Thanks in advance .....