Identify the name of above nitrogen base.

Based on the provided chemical structure:

1. The molecule is a single six-membered heterocyclic ring containing two nitrogen atoms, which identifies it as a pyrimidine base.
2. It has two carbonyl ($-C=O$) groups at positions 2 and 4, making it a 2,4-dioxopyrimidine.
3. There is no methyl group at the 5th position, which distinguishes it from thymine (5-methyluracil).
4. There is no amino group, which distinguishes it from cytosine (4-amino-2-hydroxypyrimidine).
5. Guanine is a purine base (consisting of two fused rings), so it can be ruled out immediately.

Therefore, the given structure is Uracil, which is a nitrogenous base found in RNA.

Answer: Uracil