That basically ensures that the double helix is a favorable structure. Now the only type of nonfavorable interaction is basically the interaction between the phosphate groups. So notice that this phosphate group has a negative charge, this phosphate group also has a negative charge. And when we have two light charges in close proximity, they will create a repulsive force. And so the only type of electric force, the only type of intermolecular force that tends to separate these single strands are these negative charges on these adjacent phosphate groups. So the negatively charged phosphate groups lead to electric repulsive forces.