## Core Concept
Proteins can be separated based on their physical and chemical properties. One common method for separating proteins is based on their size, which is often achieved through gel filtration chromatography or SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). However, when it comes to the options provided, focusing on a technique specifically tailored for protein separation based on size or charge is essential.

## Why the Correct Answer is Right
The correct answer, **Gel Filtration**, is a technique used for separating proteins based on their size. In gel filtration chromatography, proteins are passed through a column filled with porous beads. Smaller proteins can enter the pores of the beads and thus take a longer path through the column, while larger proteins cannot enter the pores and pass through the column more quickly. This results in the separation of proteins based on their size. This method is particularly useful for estimating the molecular weight of proteins and for purifying proteins.

## Why Each Wrong Option is Incorrect
- **Option A: Ion Exchange Chromatography** is incorrect because it separates proteins based on their charge, not size. Proteins with different charges interact differently with the charged groups on the chromatography matrix, allowing for their separation.
- **Option B: Affinity Chromatography** is incorrect because it separates proteins based on their specific biochemical interactions, such as enzyme-substrate or antigen-antibody interactions, rather than size.
- **Option D: Dialysis** is incorrect because it is used to separate molecules based on their size by diffusion through a semipermeable membrane, but it is not typically considered a method for "sorting" proteins in the same way chromatography techniques are. It's more about removing small molecules from larger ones.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **SDS-PAGE** is a powerful tool for separating proteins based on size. SDS (sodium dodecyl sulfate) denatures proteins, coating them with a negative charge proportional to their length (or molecular weight), allowing for size-based separation. This technique is widely used in molecular biology for analyzing protein mixtures.

**Correct Answer: C. Gel Filtration**