Does a bottle of acetic acid contain a solid or a liquid on a chilly morning with the window open and the laboratory at 10 ∘ c ?

Answer is:  a bottle of acetic acid contains a solid.

Acetic or ethanoic acid (CH₃COOH) when undiluted is called glacial acetic acid.

Glacial acetic acid has freezing point (melting point) around 16.6°C, so it will be at solit state.

Vinegar is mixture of acetic acid (CH₃COOH) and water (H₂O). Vinegar  is colourless liquid with sour taste and pungent smell, freezing point of the vinegar is lower than glacial acetic acid.

Acetic acid dissociate in aqueous solution to form hydrogen ions (H⁺) and acetic anion (CH₃COO⁻).

Balanced chemical reaction (dissociation):  

CH₃COOH(aq) ⇄ CH₃COO⁻(aq) + H⁺(aq).