Which of the following bases is not present in DNA?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Uracil
Nucleic acids contain two kinds of nitrogenous bases: purines (adenine and guanine) and pyrimidines (cytosine, thymine and uracil).
Option (1) Adenine — Present in DNA. A purine base found in both DNA and RNA; in DNA it pairs with thymine.
Option (2) Thymine — Present in DNA. A pyrimidine base found in DNA only; it is the base that uracil replaces in RNA.
Option (3) Cytosine — Present in DNA. A pyrimidine base found in both DNA and RNA; it pairs with guanine.
Option (4) Uracil — Not present in DNA (RNA only). Uracil is the fourth base of RNA, in place of thymine.
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 |
|---|---|---|---|---|
| – | 30-05 S2 28-05 S1 13-05 S2 | – | – | 20-08 S1 |