Two nucleic acid chains are wound about each other and held together by H bonds between pair of bases.
Adenine from two hydrogen bonds with thymine and Guanine form three hydrogen bond with cytosine.
5′G−G−C−A−A−A−T−C−G−G−C−T−A−3′
In given DNA strand total seven guanine and cytosine bases which form total 21 H -bonds and six adenine and thymine base which will form total 12 H-bonds with other DNA strand.
Total no. of H bonds =7×3+6×2=33