Final answer:
The nitro group on nitrobenzene deactivates the benzene ring by inductive effect and decreases the charge density at the ortho and para positions, increasing electron density at the meta position by resonance.
Step-by-step explanation:
In an electrophilic substitution reaction of nitrobenzene, the presence of a nitro group deactivates the benzene ring towards further electrophilic substitution. Specifically, the nitro group has an electron-withdrawing effect due to its inductive effect and resonance. The nitro group has a strong -M or -R (mesomeric or resonance) effect and a moderate -I (inductive) effect. These properties make it pull electrons away from the benzene ring, particularly affecting the ortho and para positions.
Therefore, the correct answers are: (a) The nitro group deactivates the ring by inductive effect, and (c) the nitro group decreases the charge density at ortho and para positions of the ring relative to the meta position by resonance. The <+OH> group, an example of an activating group on a benzene ring, behaves in the exact opposite manner to the nitro group. Whereas activating groups donate electron density, the nitro group withdraws it, making the meta position more favorable for reaction due to it being less deactivated than the ortho and para positions. Thus, answer (d) is also correct as the nitro group increases the electron density at the meta position relative to the ortho and para positions of the ring by resonance.