## Core Concept
The molecular size of proteins is a critical characteristic that influences their function, stability, and interactions within biological systems. Assessing the molecular size of proteins is essential in various biochemical and biotechnological applications. Techniques that can accurately determine the molecular size of proteins are vital for protein analysis.

## Why the Correct Answer is Right
The correct answer, **SDS-PAGE (Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis)**, is a widely used technique for assessing the molecular size of proteins. SDS-PAGE works by denaturing proteins with SDS, a detergent that disrupts non-covalent interactions and coats proteins with a negative charge proportional to their length (or molecular weight). When an electric field is applied, SDS-coated proteins migrate through a gel matrix, with smaller proteins moving faster and farther than larger ones. By comparing the migration distances of unknown proteins to those of standards of known molecular weight, the molecular size of the unknown proteins can be estimated.

## Why Each Wrong Option is Incorrect
- **Option A:** While certain types of chromatography can provide information on protein size, such as size exclusion chromatography, they are not primarily used for assessing molecular size in the same direct manner as SDS-PAGE.
- **Option B:** This option is not specified, but techniques like mass spectrometry can determine molecular weight precisely but are not listed; however, based on common lab practices, other methods like gel filtration can estimate size but are less commonly referenced in this context.
- **Option C:** This option is unspecified but could refer to various techniques; however, without specifics, it's challenging to directly refute, but generally, SDS-PAGE is more universally applied for size assessment.

## Clinical Pearl / High-Yield Fact
A crucial point to remember is that SDS-PAGE is a denaturing technique, meaning it disrupts the native structure of proteins. This is essential for comparing proteins based solely on size. A common pitfall is confusing SDS-PAGE with native PAGE, which separates proteins based on both charge and size without denaturation.

## Correct Answer: C. SDS-PAGE.