Which organic acid is produced when glucose is broken down without oxygen?

When glucose is broken down without oxygen, a process known as anaerobic respiration occurs. In animals, this process leads to the production of lactic acid as a byproduct. Lactic acid fermentation is particularly prominent in muscle cells when they are under strenuous conditions and oxygen supply is limited. The transformation of glucose through this pathway enables a quick release of energy, although it is less efficient than aerobic respiration.

The production of lactic acid is a key characteristic of this type of anaerobic process, and it results in the accumulation of lactic acid in the muscles, which can lead to fatigue. This is why the correct answer is lactic acid. Other organic acids mentioned, such as citric acid, acetic acid, and formic acid, do not represent the end products of anaerobic glucose breakdown in organisms like humans. Instead, they are involved in different metabolic pathways or reactions, primarily associated with aerobic pathways or different types of fermentation processes.