The coding sequences that appear in mature RNA are:

The correct answer is Option (2) → Exons

In eukaryotes the genes are split genes. The coding part of a gene is broken up by stretches that do not code. The coding pieces are called exons and the pieces in between are called introns. During splicing the introns are removed and the exons are joined, so only the exons are left in the mature (processed) RNA.

(1) Introns — Incorrect. Introns (intervening sequences) are copied into the first RNA (hnRNA) but are cut out during splicing. They do not appear in mature RNA.

(2) Exons — Correct. Exons are the coding or expressed sequences. They are joined together and appear in mature RNA.

(3) Cistrons — Incorrect. A cistron is a segment of DNA that codes for one polypeptide. It is a unit of DNA, not a part that is kept in mature RNA.

(4) Operon — Incorrect. An operon is a group of genes in bacteria that are controlled together, such as the lac operon. It is not a coding sequence of mature RNA.

Note: A similar question was also asked in CUET (UG) 2026 on 29-05-2026 (Slot 1).

NCERT Extract:
Transcription Unit and the Gene – “… In eukaryotes, the monocistronic structural genes have interrupted coding sequences – the genes in eukaryotes are split. The coding sequences or expressed sequences are defined as exons. Exons are said to be those sequence that appear in mature or processed RNA.”