MCQ Detailed View

Carbolic acid is the older common name for phenol (C₆H₅OH), an aromatic organic compound consisting of a benzene ring directly bonded to a hydroxyl group (–OH). The name "carbolic acid" was historically used because phenol was first isolated from coal tar and was acidic in nature. Although weak compared to mineral acids, phenol can still donate protons (H⁺) due to the resonance stabilization of its phenoxide ion, which explains its acidic character.

Phenol plays a very important role in both organic chemistry and applied sciences. It is a colorless to light pink crystalline solid with a distinctive odor. Historically, phenol was one of the first antiseptics used in surgery. In the 1860s, Joseph Lister used carbolic acid to sterilize surgical instruments and disinfect wounds, which marked a major advancement in antiseptic techniques and reduced infections in hospitals. This is why phenol became well-known under the name "carbolic acid."

From a chemical perspective, phenol is more acidic than simple alcohols like ethanol because the negative charge on the oxygen atom after losing a proton is stabilized by resonance with the benzene ring. However, it is less acidic than carboxylic acids such as formic acid or acetic acid.

Let us analyze the options:

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  Methanol (CH₃OH) is a simple alcohol, not carbolic acid.

  
  


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  Phenol (C₆H₅OH) is the correct answer and is commonly known as carbolic acid.

  
  


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  Formic acid (HCOOH) is the simplest carboxylic acid but not called carbolic acid.

  
  


• 
  

  Acetic acid (CH₃COOH) is vinegar’s main component, not carbolic acid.

  
  

Phenol is widely used today in the manufacture of plastics (such as Bakelite), pharmaceuticals, dyes, resins, and explosives. It remains one of the most important aromatic compounds studied in organic chemistry.

Thus, the compound known as carbolic acid is phenol (C₆H₅OH).