As the extent of electron delocalization into the ring increases, the geometry at nitrogen flattens. p-nitroaniline, for example, is planar. write a resonance contributor for p-nitroaniline that shows how the nitro group increases electron delocalization.

As the extent of electron delocalization into the ring increases, the geometry at nitrogen flattens. p-Nitroaniline, for example, is planar. Write a resonance contributor for p-nitroaniline that shows the nitro group increases electron delocalization:

This happen due to electron-withdrawing effect of Nitro group

see the attached in the image

Explanation:

What are delocalized electrons ?

The electrons present in a molecule which are not associated with a singlke atom or bond .

In benzene Ring electrons are declocalized because elctrons can be found equally on any of the six- carbons

How to show  delocalization of electron ?

1. Electron moves towards positive charge atom or away from electron-rich atom

2. The movment of electron is shown by the arrow

3. Any group which stablise the excess charge, will increase the delocalization

Delocalisation of Aniline : look at the attached image

In free - NH3 group , The electron Pair (lone pair) of Nitrogen are easily available for donation and NH3 act as base. It has pyramidal shape

But in aniline ( one H  of NH3 is replaced by the  benzene ring ):

lone-pair of Nitrogen are deloclized over the benzene ring. Hence NH2- group become planar (flattened) and comes in the plane of benzene. The lone pair of  electrons increase the electron density at ortho and para position of the benzene ring .

In  p-Nitroaniline

Nitro(NO2)- group is present at the para position with respect to -NH2 This NO2- group is electron withdrawing in nature.Electron - withdrawing : those groups that draws the electron density towards themself . Hence they stablise the negative charge.NO2- stablises the increased electron density created by -NH2 of aniline . Hence it increases the electron delocalization

And a) oxygen i believe

Thermohaline circulation and gyres