How many hydrogen bonds are there between adenine and thymine in the DNA double helix?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 2
In the DNA double helix the two strands are held together by hydrogen bonds between specific base pairs. In Fig. 10.7 each A–T pair is drawn with a double line (A=T, two hydrogen bonds), and each G–C pair with a triple line (G≡C, three hydrogen bonds).
NCERT (2026-27 edition):
10.5.2 Structure of Nucleic Acids – “… James Watson and Francis Crick gave a double strand helix structure for DNA (Fig. 10.7). Two nucleic acid chains are wound about each other and held together by hydrogen bonds between pairs of bases. … Adenine forms hydrogen bonds with thymine whereas cytosine forms hydrogen bonds with guanine.”
Fig. 10.7: Double strand helix structure for DNA