The amino group is ortho, para directing and powerful activating substituent so that aryl amines undergo the typical electrophilic substitution reactions readily. In fact, the rate of these reactions is so great that in certain cases poly-substitution, rather than mono-substitution occurs, even under mild conditions. If the reactions in such cases have have to be arrested at the mono-substitution stage, the activating influence of the –NH₂ group has to be arrested.

Identify the product of the given reaction. 

p-Aminobenzenesulphonic acid 

The correct answer is option 1. p-Aminobenzenesulphonic acid.

When aniline \((C_6H_5NH_2)\) undergoes sulphonation, the major product is p-aminobenzenesulphonic acid, commonly known as sulphanilic acid.

The sulfonation of aniline involves reacting it with concentrated sulfuric acid \((H_2SO_4)\). The amino group \((NH_2)\) is a strong activator and directs the incoming sulfonic acid group \((SO_3H)\) primarily to the ortho and para positions. However, due to steric hindrance, the para position is typically favored, leading to the major product being para-substituted.

Here is the reaction:

Aniline reacts with sulphuric acid to form the anilinium ion \((C_6H_5NH_3^+)\), which is more stable under the acidic conditions. The anilinium ion then undergoes electrophilic aromatic substitution with sulfur trioxide \((SO_3)\) formed in situ from sulphuric acid, leading to the formation of the para-substituted product. The resulting product is neutralized to form sulphanilic acid. So, the major product of sulfonation of aniline is p-aminobenzenesulphonic acid (sulphanilic acid).