The two strands of DNA are held together by -
Ans. is 'b' i.e. hydrogen bonds : In the double helix, the two chains are coiled around a common axis in an antiparallel manner that is, the 5C end of one strand is paired with the end of the other strand.The bases of one strand are paired with the bases of the second strand so that an adenine is always paired with a thymine, whereas a cytosine is always paired with a guanine. The base pairs are held together by hydrogen bonds : 2 between A and T*3 between G and C*
Van-der-Waal bond
hydrogen bond
Covalent bond
Ionic interaction