(a) DNA stands for Deoxyribose Nucleic Acid which is present in chromosomes.
(b) DNA has a double helical or spiral structure having nucleotides. Nucleotides comprises of phosphoric acid, deoxyribose sugar and nitrogeneous bases like adenine, thymine, guanine and cytosine. The nucleotide sequence of the DNA molecule is called a gene. Genes are present on DNA. Changes in the genes can alter the characteristics of any organism.
(c) The double helical, spiral structure of DNA was proposed by James D. Watson and Francis Crick in 1953 for which they were awarded the Noble prize.