Mature mRNA is a fully processed ___________.

The correct answer is Option (1) → hnRNA

In eukaryotes RNA polymerase II first makes a precursor of mRNA, the heterogeneous nuclear RNA (hnRNA). It is processed by splicing (introns removed), capping and tailing.

Option (1) hnRNA — Correct. In eukaryotes the primary transcript, hnRNA (heterogeneous nuclear RNA), contains both exons and introns. It undergoes splicing, capping and tailing, and the fully processed hnRNA is the mature mRNA.

Option (2) snRNA — Incorrect. Small nuclear RNA is a separate RNA made by RNA polymerase III; it is not processed into mRNA.

Option (3) 28S RNA — Incorrect. 28S rRNA is a ribosomal RNA, made by RNA polymerase I.

Option (4) 5srRNA — Incorrect. 5S rRNA is also a ribosomal RNA, made by RNA polymerase III.

NCERT Extract:
Types of RNA and the Process of Transcription – “… hnRNA undergoes additional processing called as capping and tailing. In capping an unusual nucleotide (methyl guanosine triphosphate) is added to the 5’-end of hnRNA. In tailing, adenylate residues (200-300) are added at 3’-end in a template independent manner. It is the fully processed hnRNA, now called mRNA, that is transported out of the nucleus for translation (Figure 5.11).”