In organic chemistry and medicine, which compound is commonly known as carbolic acid?

Introduction / Context:
Many organic compounds have traditional common names that reflect their early uses in medicine and industry. Carbolic acid is one such historical name, especially associated with antiseptic use in surgery. Modern chemistry uses systematic names, but examinations still ask students to match old common names with their modern equivalents. This question asks which compound is known as carbolic acid.

Given Data / Assumptions:

• The options include phenol, ethanol, acetic acid, oxalic acid, and formic acid.
• Carbolic acid was historically used as an antiseptic.
• The correct answer should match both the functional group and the historical usage.
• We assume basic familiarity with the formulas and uses of these simple organic compounds.

Concept / Approach:
Carbolic acid is the older name for phenol, which has the formula C6H5OH. It consists of a benzene ring with a hydroxyl group and has antiseptic properties. Joseph Lister famously used carbolic acid spray to reduce infections during surgery in the nineteenth century. Ethanol is common alcohol in beverages and sanitiser, acetic acid is vinegar acid, oxalic acid is a dicarboxylic acid found in some plants, and formic acid is the simplest carboxylic acid found in ant venom. None of these is called carbolic acid.

Step-by-Step Solution:
Step 1: Recall that carbolic acid was used historically as a disinfectant and antiseptic in hospitals. Step 2: Remember that this carbolic acid is phenol, a benzene ring with an –OH group. Step 3: Recognise that ethanol is simply common alcohol, not normally called carbolic acid. Step 4: Know that acetic, oxalic, and formic acids are carboxylic acids with different formulas and uses. Step 5: Choose phenol as the compound that corresponds to the name carbolic acid.

Verification / Alternative check:
Textbooks on organic chemistry and medical history state that phenol was known as carbolic acid and used as one of the first antiseptics in surgery. Its older industrial names include acidum carbolicum and hydroxybenzene. Ethanol is labelled as ethyl alcohol, acetic acid as ethanoic acid, and oxalic and formic acids by their own names, not as carbolic acid. These sources confirm the correct identification.

Why Other Options Are Wrong:
Ethanol is a primary alcohol used in beverages and sanitisers, but it is not called carbolic acid. Acetic acid is the main acid in vinegar and is known by that name. Oxalic acid is a stronger dicarboxylic acid found in plants like spinach, and formic acid is in ant stings and some industrial processes. None of these have the aromatic hydroxyl structure or historical name associated with phenol.

Common Pitfalls:
Students sometimes confuse different acids because of overlapping uses as disinfectants or preservatives. Another common error is to assume that any compound ending in "ol" must be an alcohol and not an acid, forgetting that old names like carbolic acid do not follow modern naming rules. To avoid confusion, memorise a few historic names clearly, such as carbolic acid for phenol and wood spirit for methanol, and you will be able to answer such questions reliably.

Final Answer:
The compound commonly known as carbolic acid is phenol.