In this reaction, the alkyl chain is oxidized to carboxylic acid in presence of oxidants like KMnO₄ or chromic acid irrespective of the number of carbon atoms in the chain.

Introduction:
n-Butylbenzene is a compound with a butyl group attached to the benzene ring. On oxidation, it undergoes a reaction called side-chain oxidation, where the alkyl group is oxidized to form a carboxylic acid. The specific product formed depends on the conditions of the reaction.

Explanation:
The oxidation of n-butylbenzene can proceed through different pathways, resulting in different products. However, in this case, the correct answer is option 'A', which states that the product is benzoic acid. Let's explore why this is the case.

Side-chain oxidation:
Side-chain oxidation involves the oxidation of the alkyl group attached to the benzene ring. In the case of n-butylbenzene, the butyl group (C4H9) is oxidized.

Reagents:
The reagents used for the oxidation of n-butylbenzene can vary. Common oxidizing agents include potassium permanganate (KMnO4) and chromic acid (H2CrO4).

Reaction conditions:
The reaction conditions also play a crucial role in determining the product. In this case, we assume that the reaction is carried out under controlled conditions to favor the formation of benzoic acid.

Product formation:
Under controlled conditions, n-butylbenzene undergoes oxidation to form benzoic acid. The butyl group (C4H9) is oxidized to a carboxylic acid group (-COOH) attached to the benzene ring, resulting in the formation of benzoic acid (C6H5COOH).

Other possible products:
It is worth noting that under different reaction conditions, other products can also be formed. For example, if the reaction is carried out under harsher conditions or with a different oxidizing agent, the butyl group can be further oxidized to form butanoic acid (C3H7COOH) instead.

Conclusion:
In summary, the oxidation of n-butylbenzene can result in different products depending on the reaction conditions. However, under controlled conditions, it primarily forms benzoic acid.