Concept:Two DNA strands are held together by weak hydrogen bonds between complementary nitrogenous bases.
Explanation:DNA is a double helix made of two strands linked by base pairing.
Adenine pairs with thymine, and guanine pairs with cytosine.
These complementary bases attract each other using hydrogen bonds.
An
A−T pair forms two hydrogen bonds, while a
G−C pair forms three hydrogen bonds.
Hence, the bond that holds the bases of the two DNA strands together is not covalent or electrovalent; it is a hydrogen bond.
Answer:The correct option is B. hydrogen bond.