Final answer:
The double-helical conformation of DNA is maintained by hydrogen bonds between nitrogenous bases and van der Waals forces that stabilize the strands, with hydrogen bonds being particularly important in stabilizing base pairs. The correct option is B.
Step-by-step explanation:
The noncovalent interactions involved in maintaining the double-helical conformation of DNA are hydrogen bonds and van der Waals forces. Hydrogen bonds occur between the nitrogenous bases on opposite strands of the DNA, stabilizing the base pairs.
Adenine (A) pairs with thymine (T) through two hydrogen bonds, while cytosine (C) pairs with guanine (G) through three hydrogen bonds. Van der Waals forces are weaker interactions that help to stabilize the positioning of the DNA strands as they wind around each other in the helix.
It is critical to recognize that phosphodiester bonds form the backbone of the DNA strands through covalent bonds between the phosphate group and the sugar molecule, but they are not considered noncovalent interactions. Thus, the correct answer to the question is B. Hydrogen bonds and van der Waals forces.