Which lane's sample produced the fewest fragments of dna?

The correct answer is Lane A.

The smallest fragments of DNA will be witnessed near the bottom of the gel, on the other hand, the heavier fragments will be visible at the top. The theory behind this is there is a specific pore size on the basis of the concentration of acrylamide/agarose in the gel.

Irrespective of the size of the pore, the smaller fragments will exhibit an easier time traveling through the gel in comparison to the larger fragments for a specific pore size. While, eventually, the size is typically determined by running a ladder with particular, known molecular weight markers.