Answer:
DNA is polar due to its highly charged phosphate backbone. Its polarity makes it water-soluble (water is polar) according to the principle "like dissolves like". ... This fact makes water a very good solvent for charged compounds like salts.
Your DNA's sugar phosphate backbone is charged. By adding salt, we help neutralize the DNA charge and make the molecule less hydrophilic, meaning it becomes less soluble in water. The salt also helps to remove proteins that are bound to the DNA and to keep the proteins dissolved in the water.
It is well known that Ethanol has a lower dielectric constant than water, making it to promote ionic bond formations between the Na+ (from the salt) and the PO3- (from the DNA backbone), further, causing the DNA to precipitate.
Explanation:
Ideally DNA needs to be precipitated with pellet and should not remain in supernatant. DNA is acidic in nature and therefore, needs optimum salt concentration in the buffer to be pelleted from a solution. At very low salt concentration or without salt DNA would remain in supernatant.
