Draw the structure of the major organic product of the following reaction.
Concepts and reason
This problem is based on the concept of oxidation reaction of organic compounds.
Organic compounds containing benzene ring can be oxidized by various methods in order to give a variety of compounds like phenolic compounds, carbonyl compounds and carboxylic compounds.
Fundamentals
Potassium permanganate 
in acidic condition is used to oxidize aromatic compounds such as toluene to carboxylic acids.
Answer:
The structure of reactant is given below:
Explanation:
This compound has two rings in which one ring is aliphatic and the other one is aromatic ring and one methyl group is attached at the aromatic ring.
The complete reaction sequence is given below:
Explanation:
The reactant has one benzene ring and aliphatic substituents attached to it. Thus, aliphatic carbons directly attached to the benzene ring are oxidized with the treatment of Potassium permanganate 
in acidic condition in order to form a compound containing carboxylic group.