Vinegar used in cooking contains which of the following compounds?

Acetic acid

The correct answer is option 4. Acetic acid.

Vinegar used in cooking contains acetic acid.

Acetic acid is the main component of vinegar. It is responsible for the sour taste and distinctive odor of vinegar. When acetic acid is dissolved in water, it forms vinegar. Therefore, option 4, acetic acid, is the correct answer.