Gel electrophoresis sorts dna molecules on the basis of their

Size and charge and speed

Explanation:

Gel electrophoresis  is method designed for the separation of DNA molecules. The are also used to separate other micromolecules like RNA and protein, etc. This separation takes place based on their size and charge. The molecule travels through the gel in all different directions but their speed are different and thus they are separated.

the answer is neither ball has a charge.

because if they were both positively charged, they will repel each other.

if they were positively and negatively charged, they will seek.