Question

Why does NO2 group shows its effect at ortho and Para positions but not ar meta position

Answer 1

Where will the attacking reagent attack? Yes, right. Wherever it will get electron-deficient (cationic) site there it will attack with its electron cloud, forming a bond. Now to check where this attack will be favoured, we need to know where the electron-deficient sites are formed. To do so let's make resonance structures.

Clearly the charge appears on ortho and para positions, and that’s why the nitro group is ortho- and para-directive in nature.

Hope this helps. Thanks for reading.

:)