The base which is not present in RNA is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → thymine
The nitrogenous bases of nucleic acids are purines (adenine, guanine) and pyrimidines (cytosine, thymine, uracil).
Option (1) adenine — Present in RNA. A purine with an –NH2 group.
Option (2) guanine — Present in RNA. A purine with a C=O and an –NH2 group.
Option (3) cytosine — Present in RNA. A pyrimidine with an –NH2 group.
Option (4) thymine — Not present in RNA. A pyrimidine with two C=O groups and a methyl group on the ring (5-methyluracil); it occurs in DNA, while RNA has uracil in its place.
NCERT (2026-27 edition):
Chemical Composition of Nucleic Acids – …
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| 29-05 S1 20-05 S2 | – | – | – | – |