Question

Which nitrogen base is this?

• A. Cytosine
• B. Thymine
• C. Adenine
• D. Uracil

Answer 1

The correct option is A Cytosine

Cytosine is a pyrimidine which has single ring structure which has nitrogen at 1 and 3 position. It has an amine group at position 4 and a keto group at position 2. C${}_4$H${}_5$N${}_3$O is the molecular formula of cytosine. It pairs with the guanosine by three hydrogen bonds.

So, the correct answer is option A.