**Core Concept**
Ion exchange chromatography is a laboratory technique used to separate, identify, and quantify each component in a mixture. It relies on the principle of ionic interactions between molecules and a stationary phase, which can be either positively or negatively charged.

**Why the Correct Answer is Right**
In ion exchange chromatography, the stationary phase is typically a resin with a fixed ionic charge, whereas the mobile phase contains molecules with the opposite charge. When negatively charged molecules in the sample interact with the positively charged stationary phase, they are retained. Conversely, when positively charged molecules in the sample interact with the negatively charged stationary phase, they are also retained. However, when negatively charged molecules in the sample interact with the positively charged stationary phase, they are selectively released into the positively charged mobile phase, allowing for their separation and identification.

**Why Each Wrong Option is Incorrect**
* **Option A:** Size exclusion chromatography separates molecules based on their size, not charge, making it an incorrect choice.
* **Option B:** Affinity chromatography relies on specific interactions between molecules and a ligand, not ionic charge, making it an incorrect choice.
* **Option D:** High-performance liquid chromatography (HPLC) is a broad term that encompasses various chromatographic techniques, including ion exchange chromatography, but it is not a specific method that selectively releases negatively charged molecules into a positively charged mobile phase.

**Clinical Pearl / High-Yield Fact**
Ion exchange chromatography is widely used in various fields, including biochemistry, pharmacology, and medicine, to separate and analyze complex mixtures of molecules. Understanding the principles of ion exchange chromatography is essential for interpreting laboratory results and making informed decisions in clinical and research settings.

**Correct Answer:** C.