MCQ Detailed View

Lactic acid is the common name for 2-hydroxypropanoic acid, an organic compound with the molecular formula C₃H₆O₃. It belongs to the class of hydroxycarboxylic acids, which means the molecule contains both a hydroxyl group (-OH) and a carboxylic acid group (-COOH). In lactic acid, the hydroxyl group is attached to the second carbon atom of the three-carbon chain, hence the systematic IUPAC name 2-hydroxypropanoic acid.

The importance of lactic acid in chemistry and biology is significant. It is a key product of anaerobic respiration in muscles, where glucose is broken down without oxygen. This process leads to lactic acid accumulation, which causes temporary muscle fatigue and soreness. Lactic acid is also produced naturally in fermented foods such as yogurt, sauerkraut, and kimchi through the action of lactic acid bacteria.

Looking at the options:

• 
  

  3-Hydroxypropanoic acid is not lactic acid because its hydroxyl group is on the third carbon, not the second.

  
  


• 
  

  2-Hydroxybutanoic acid has four carbons in the main chain, so it is a different compound.

  
  


• 
  

  3-Hydroxybutanoic acid is another four-carbon hydroxy acid, unrelated to lactic acid.

  
  

Only 2-hydroxypropanoic acid corresponds to lactic acid. Its structure consists of a central carbon atom connected to a hydroxyl group, a hydrogen atom, a methyl group (-CH₃), and a carboxylic acid group. Because of this arrangement, lactic acid is also a chiral molecule, existing in two enantiomeric forms: L-lactic acid and D-lactic acid. The L-form is the one commonly found in human metabolism.

Lactic acid is widely used in the food industry as a preservative and flavoring agent, in the pharmaceutical industry for drug formulations, and in the polymer industry for producing biodegradable plastics such as polylactic acid (PLA).