Answer:
The DNA (deoxyribonucleic acid) is a double stranded molecule function as a genetic material in many organisms. It is comparatively stable molecule than RNA because of hydrogen bonds found in it and also due to lack of an oxygen atom. It's basic unit is nucleotide which comprises of a nitrogenous base, ribose sugar and a phosphate group. There are four type of nitrogenous bases found in DNA known as Purines (guanine +adenine) and pyrimidines (cytosine + thymines). As the name indicates the purines are double ringed while pyrimidines are single ringed.
This question is based on the concepts of watson and crick model of DNA. According to which base form bonds with their complementary bases like adenine form double hydrogen bond with thymine and cytosine form triple hydrogen bond with thymine.
Hydrogen bonding is function of hydrogen in which it form bond with atoms of higher electronegativity (ability to attract the bonding pair) like oxygen.
