(a) Structures for ethanol and ethanoic acid are as follows:
(i)

H− H | C | H − H | C | H −O−H

Ethanol

(ii)

H− H | C | H − O || C

Ethanoic acid

(b) Conversion of ethanol to ethanoic acid is considered as an oxidation reaction because oxygen is added to ethanol to convert it to ethanoic acid.
In the above reaction alkaline KMnO4 or acidified K2Cr2O7 adds oxygen to ethanol hence they are the oxidising agent used in the reaction involved.