Why is restriction-cut DNA run on a gel?

Correct answer: To separate DNA fragments by size

After restriction digestion, one DNA molecule may be converted into fragments of different lengths. Agarose gel electrophoresis separates these charged DNA fragments mainly according to size: when an electric field is applied, DNA moves toward the positive electrode, and smaller fragments generally migrate through the gel matrix faster and farther than larger fragments. The resulting bands reveal the restriction pattern and allow comparison or approximate size estimation with a DNA ladder. Therefore option B is correct. Gel electrophoresis does not multiply the enzyme, convert DNA into sugar, or dissolve protein; those statements confuse separation with unrelated biochemical processes.