Question

which charge is present on DNA and why

Answer 1

A single nucleotide that make up DNA are composed of a nucleobase (adenine, thymine, etc.), a sugar (generally ribose), and a mono-, di-, or tri-phosphate group. Since phosphate groups are negatively charged, DNA becomes negative charge too. DNA actually acquires its negative charge by dissociating into phosphate esters. DNA being negatively charged and is bound to positively charged histone protein and thus also has a negatively charged backbone.