In ii where is -i effect ...?

Sp2 carbon are more eletronegative than sp3 carbon. Compare the %s character. More the 's' character more will be eletronegativity. sp2 has more % s

Halogen shows -I effect while Alkyl group shows +I effect

hope this will help you 🙏

I means inductive effect. -I means eletron withdrawing & +I is eletron donating.

we are just compairing here.actually here double bonded Carbon is present that is sp2 hybridised do it pull the electrons towards itself and show - I effect