What gel is used for DNA separation?

Agarose gel is used for DNA separation. This gel has been found to be most effective for separating DNA fragments between100 bp and 25 kb.

Agarose gel is essentially a polysaccharide. It comes as dry, powdered flakes. When heated in a buffer composed of water containing some salts and then allowed to cool, it forms a gel that is solid but slightly squishy. 

At the molecular level, agarose gel is composed of a matrix of agarose molecules held together by hydrogen bonds. Wells, which are pocket-like indentations, form at one end of the gel. DNA samples are placed in these wells.