How to get the hybridization of N IN NO2- ?

Answer 1

I do it as an after the fact method.
Draw the Lewis dot structure.
1 N = 1 x 5 electrons = 5 e
2 O = 2 x 6 e = 12 e
1 e for charge = 1 e
total electrons = 18.

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:N=O

Now place 3 pairs e (6 electrons total) around top O and 2 pairs around side O. That should use up the 18.
Count the regions of high electron density. There are 3 (1 for double bond, 1 for single bond, and 1 for unpaired set electrons on N. Three regions of high electron density = trigonal planar arangement and sp2 hybridization.