Short answers, pulled from the story.
Acetic acid is an acidic, colourless liquid organic compound and the active component of vinegar. It is produced naturally by acetic acid bacteria of the genus Acetobacter, which are found universally in foodstuffs, water, and soil, causing fruits and other foods to spoil with a sour character.
Vinegar, the dilute form of acetic acid, has been used for at least 10,000 years. Its use in alchemy extends to the third century BCE, when Theophrastus described how it acted on metals to produce artistic pigments.
About 75% of industrial acetic acid is produced by the carbonylation of methanol, predominantly via the iridium-catalyzed Cativa process introduced by BP Chemicals in the late 1990s. Global production reached 17.88 million metric tonnes per year as of 2023.
The largest single industrial use of acetic acid is in the production of vinyl acetate monomer, which consumed an estimated third of world production as of 2008. It is also used to make acetic anhydride for cellulose acetate and photographic film, and as a solvent for inks, paints, and coatings via ester production.
The acetyl group derived from acetic acid is fundamental to all forms of life. Bound to coenzyme A, it is central to the metabolism of carbohydrates and fats. Acetic acid is also a component of vaginal lubrication in humans and other primates, where it appears to act as a mild antibacterial agent.
Prolonged inhalation at 10 parts per million can irritate the eyes, nose, and throat; at 100 ppm, marked lung irritation and possible tissue damage may result. Concentrated solutions of 25% or more are corrosive to skin, and burns may not appear until hours after contact.