## **Core Concept**
The DNA double helix structure is stabilized by various types of chemical bonds and interactions. The primary forces maintaining the double helix are hydrogen bonds between the nucleotide bases and hydrophobic interactions.

## **Why the Correct Answer is Right**
The correct answer, , refers to hydrogen bonds. These are crucial for maintaining the DNA double helix structure. Hydrogen bonds form between the bases of the two DNA strands: adenine (A) pairs with thymine (T) through two hydrogen bonds, and cytosine (C) pairs with guanine (G) through three hydrogen bonds. This base pairing is essential for the stability and replication of DNA.

## **Why Each Wrong Option is Incorrect**
- **Option A:** - This option is incorrect because covalent bonds, although present in the DNA backbone (phosphodiester bonds), do not directly contribute to the maintenance of the double helix structure between the two strands.
- **Option B:** - This option is incorrect as van der Waals forces, while contributing to the overall stability of DNA, are not the primary forces maintaining the double helix structure.
- **Option D:** - This option is incorrect because disulfide bonds are not involved in the structure of DNA; they are more commonly associated with protein structure.

## **Clinical Pearl / High-Yield Fact**
A crucial point to remember is that the specificity of base pairing (A-T and G-C) is fundamental to DNA replication and transcription. This specificity is ensured by the hydrogen bonding between the bases.

## **Correct Answer:** . Hydrogen bonds.