The compound formed as a result of oxidation of ethyl benzene by $$KMnO_4$$ is

Alkyl side-chains attached to an aromatic ring that contain at least one benzylic hydrogen are oxidised by strong oxidising agents such as alkaline or acidic $$KMnO_4$$ to a single product: the carboxylic acid $$\left(-COOH\right)$$ derivative of the ring, irrespective of the length of the side chain.

Ethyl benzene is $$C_6H_5CH_2CH_3$$. The benzylic carbon (the $$CH_2$$ directly bonded to the ring) possesses benzylic hydrogens, so it is susceptible to oxidation.

On treatment with hot, acidic or basic $$KMnO_4$$:

$$C_6H_5CH_2CH_3 \;\xrightarrow[\text{heat}]{KMnO_4} \; C_6H_5COOH + CO_2 + H_2O$$

The entire side-chain—here $$CH_2CH_3$$—is ultimately cleaved down to one carbon attached to the ring, which is converted into the carboxyl group $$-COOH$$. Hence the aromatic product is benzoic acid $$C_6H_5COOH$$.

Checking the options:
Option A: benzophenone - requires oxidation of two phenyl rings attached to a carbonyl; not formed here.
Option B: acetophenone - has a carbonyl group but no oxidising pathway from ethyl benzene under these conditions.
Option C: benzoic acid - matches the reaction product.
Option D: benzyl alcohol - is formed by mild reduction, not oxidation.

Therefore, the compound obtained is benzoic acid.

Option C which is: benzoic acid