**Core Concept**
Racemization refers to the process by which an optically pure enantiomer is converted into a racemic mixture, where equal amounts of both dextro (D-) and levo (L-) forms are present. This phenomenon involves the conversion of a chiral molecule to its non-superimposable mirror image, resulting in a loss of optical activity.

**Why the Correct Answer is Right**
Racemization occurs through various mechanisms, including acid-catalyzed hydrolysis of esters, base-catalyzed hydrolysis of amides, and thermal isomerization. These reactions involve the breaking of bonds and the formation of new ones, leading to the conversion of the optically pure enantiomer into a racemic mixture. The process of racemization is significant in biochemistry, as it affects the activity and efficacy of various biologically active compounds.

**Why Each Wrong Option is Incorrect**
**Option A:** Polymerization refers to the process of combining monomers to form a polymer, which is unrelated to the conversion of an optically pure enantiomer into a racemic mixture.

**Option B:** Stereoisomerism refers to the phenomenon of molecules having the same molecular formula and sequence of bonded atoms but differing in their three-dimensional arrangement. While related to the concept of enantiomers, stereoisomerism is a broader term that encompasses multiple types of isomers, not just those resulting from racemization.

**Option D:** Fractionation refers to the process of separating a mixture into its individual components based on differences in their physical or chemical properties. This is unrelated to the conversion of an optically pure enantiomer into a racemic mixture.

**Clinical Pearl / High-Yield Fact**
It's essential to note that racemization can affect the efficacy and safety of various pharmaceuticals, as the conversion of an optically pure enantiomer to a racemic mixture can alter the drug's pharmacokinetics and pharmacodynamics. This highlights the significance of understanding racemization in the context of biochemistry and pharmacology.

**✓ Correct Answer: C. c) Racemization**