The correct option is: (a) Adenine has 4 free nitrogen atoms
Explanation:
Nitrogen containing organic ring compounds are present in the nucleotides of nucleic acid. They are of two types two ringed nitrogenous compounds e.g., adenine and guanine and single ringed nitrogenous compounds e.g., cytosine and thymine. Purines are 9-membered double rings and each has four N-atoms at 1',3'. 7' and 9' positions. A pyrimidine has two N-atoms at 1' and 3' positions.
