Explanation

Thymine is the nitrogenous base which is not present in RNA

Thymine is one of the four nucleobases found in DNA (along with adenine, guanine, and cytosine)

Whereas RNA contains uracil (U) instead of thymine.

RNA uses uracil as a complementary base to adenine during transcription,

while DNA uses thymine as a complementary base to adenine during replication.