The correct structures of A and B formed in the following reactions are:

The correct answer is p-aminophenol for A and N-(4-hydroxyphenyl)acetamide for B.

According to NCERT Class 12 Chemistry, Chapter 13: Amines:

"Nitro compounds are reduced to amines by passing hydrogen gas in the presence of finely divided nickel, palladium or platinum." "Primary and secondary amines react with acid chlorides, anhydrides and esters by nucleophilic substitution reaction. This reaction is known as acylation."

The given reaction sequence proceeds through the following steps:

First, the starting material, p-nitrophenol, undergoes catalytic hydrogenation using H₂ and a palladium catalyst in ethanol. This reducing agent selectively reduces the nitro group (-NO₂) to an amino group (-NH₂). The phenolic hydroxyl group (-OH) is not reduced under these conditions. Thus, product A is p-aminophenol, a benzene ring with an -OH group and an -NH₂ group at para positions.

Next, intermediate A is treated with 1.0 equivalent of acetic anhydride. p-Aminophenol contains two nucleophilic functional groups: the amino group (-NH₂) and the phenolic hydroxyl group (-OH). Because nitrogen is less electronegative than oxygen, it holds its lone pair of electrons less tightly, making the -NH₂ group a stronger nucleophile than the -OH group.

Since only one equivalent of the acylating agent (acetic anhydride) is provided, selective acetylation occurs at the more reactive site. The stronger amine nucleophile attacks the acetic anhydride, converting the -NH₂ group into an acetamido group (-NHCOCH₃). The less reactive -OH group remains unaffected.

Therefore, the major product B is N-(4-hydroxyphenyl)acetamide, where the original nitro group has been fully transformed into an amide, while the starting hydroxyl group remains intact.