Which of the following substances could be classified under oxidizing agents?

Potassium dichromate is classified as an oxidizing agent because it contains chromium in a high oxidation state, specifically +6. In chemical reactions, oxidizing agents are substances that can accept electrons from other species, thereby causing those species to be oxidized. Potassium dichromate can facilitate the oxidation of other substances while itself is reduced to a lower oxidation state, typically chromium(III). This property makes it very effective in redox reactions, such as in the oxidation of alcohols or other organic compounds.

The other substances listed do not possess strong oxidizing properties. Acetic acid is a weak acid that does not have the capability to act as an oxidizing agent. Sodium metal is a strong reducing agent since it readily donates electrons. Ethylene glycol, which is a viscous fluid commonly used as an antifreeze, does not exhibit oxidizing behavior either. These properties help clarify why potassium dichromate stands out as the correct answer.