Purine base found in RNA is

The correct answer is Guanine.

Step-by-step Explanation:

1. Nitrogenous bases in nucleic acids (DNA and RNA) are categorized into two structural families:
- Purines: Characterized by a double-ring nitrogenous structure. The primary purines are Adenine (A) and Guanine (G).
- Pyrimidines: Characterized by a single-ring nitrogenous structure. The pyrimidines are Cytosine (C), Thymine (T), and Uracil (U).

2. Let us look at the nitrogenous bases present in RNA (Ribonucleic Acid):
- Purine bases: Adenine (A) and Guanine (G)
- Pyrimidine bases: Cytosine (C) and Uracil (U)

3. Let us evaluate each option based on this classification:
- Guanine: This is a purine base and is found in RNA. (Correct)
- Cytosine: This is a pyrimidine base.
- Thymine: This is a pyrimidine base (principally found in DNA).
- Uracil: This is a pyrimidine base.

Therefore, the only purine base among the choices that is present in RNA is Guanine.