Identify the following compound.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Uracil
The structure is a pyrimidine ring (one six-membered ring with two N atoms) carrying two C=O groups (at C-2 and C-4), two N–H groups and no methyl and no amino group. This is uracil, the base found in RNA in place of thymine.
Why the other options are incorrect
Option (2) Thymine — Incorrect. Thymine is 5-methyluracil; it has a \( \ce{CH3} \) group at C-5, which the given structure lacks.
Option (3) Cytosine — Incorrect. Cytosine has an \( \ce{NH2} \) group at C-4 and only one C=O group.
Option (4) Guanine — Incorrect. Guanine is a purine with two fused rings (six- and five-membered), not a single six-membered ring.
NCERT (2026-27 edition):
Chemical Composition of Nucleic Acids – “… DNA contains four bases viz. adenine (A), guanine (G), cytosine (C) and thymine (T). RNA also contains four bases, the first three bases are same as in DNA but the fourth one is uracil (U).”
