The correct option is B thymine
The nitrogenous base present in DNA and not in RNA is thymine.
There are two types of nitrogenous bases found in DNA and RNA. They are purines and pyrimidines.
Purines consist of adenine and guanine.
Pyrimidines consist of cytosine, uracil and thymine.
Both adenine and guanine can be found in DNA and RNA. But, among pyrimidines, DNA consists of cytosine and thymine, and RNA consists of cytosine and uracil.