When wine is exposed to air it becomes sour due to:
A. Oxidation of $C_{2} H_{5} O H$ into $C H_{3} C O O H$
B. Bacteria
C. Virus
D. Formic acid formation

Answer

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Hint: When a substance is exposed to air, oxygen in the air combines with the substance to form oxides and this process is known as oxidation. Alternatively, oxidation is defined as the process of the addition of oxygen or we can say that the process involves the removal of hydrogen or any other electropositive atom.

Complete step by step answer:
When wine is exposed to air for a long time it becomes sour because the aerobic bacteria allows the oxidation of ethanol into ethanoic acid and water. The chemical reaction involved is given as:

C_{2} H_{5} O H \overset{O x i d a t i o n}{\to} C H_{3} C O O H

The steps involved in the process are:
The ethanol available in wine is oxidized partially to ethanal.
The partially oxidised ethanal is oxidized to ethanoic acid.

So, the correct answer is Option A.

Additional Information:
The characteristic taste of wine tends to lose when it is exposed to air, but this is not the case with all the wines, it has been noticed that some of the expensive wines prepared with sophisticated processes tend to get much richer taste rather than the sour taste over a period of time.

Note: When wine is exposed to air, it tends to get the vinegar taste as fermentation is normally an oxygen-free process as carbon dioxide is released when yeast turns the sugar in the grape juice to alcohol. When exposed to the air, the bacteria tend to change the sugar to acetic acid. This process is known as aerobic fermentation. The resultant wine is not just wine it is wine vinegar.