Introduction:
P-nitrophenol and o-nitrophenol are two isomers of nitrophenol. They differ in the position of the nitro group (-NO2) on the phenol ring. The acidity of these compounds can be explained based on the electronic and steric effects of the substituents.

Electronic Effects:
The nitro group is an electron-withdrawing group due to its strong electronegativity. It exerts an inductive effect, withdrawing electron density from the phenol ring. This electron withdrawal destabilizes the phenoxide ion formed during deprotonation, making the compound more acidic.

Steric Effects:
The steric effect refers to the influence of bulky groups on the reactivity of a molecule. In the case of p-nitrophenol, the nitro group is positioned at the para position, which is further away from the hydroxyl group (-OH). This allows for less steric hindrance during deprotonation, making it easier for the hydroxide ion to abstract the proton.

Resonance Stabilization:
The phenoxide ion formed after deprotonation can undergo resonance stabilization. In p-nitrophenol, the negative charge is delocalized over the entire phenol ring, which stabilizes the ion. On the other hand, o-nitrophenol has a greater tendency to form a localized negative charge on the oxygen atom, resulting in less resonance stabilization.

Overall Comparison:
Considering the electronic effects, steric effects, and resonance stabilization, p-nitrophenol is more acidic than o-nitrophenol. The electron-withdrawing nature of the nitro group destabilizes the phenoxide ion, while the para position of the nitro group reduces steric hindrance during deprotonation. Additionally, the resonance stabilization of the phenoxide ion in p-nitrophenol further enhances its acidity.

Summary:
In summary, p-nitrophenol is more acidic than o-nitrophenol due to the combined effects of the electron-withdrawing nature of the nitro group, reduced steric hindrance, and enhanced resonance stabilization of the phenoxide ion. These factors contribute to the easier deprotonation of p-nitrophenol compared to o-nitrophenol.