Provide definitions and explanations for the following terms: Exons,Introns,Capping,and Tailing.

(N/A) Exons: These are coding sequences or expressed sequences that appear in mature or processed $RNA$.
Introns: These are intervening sequences which do not appear in mature or processed $RNA$. They only interrupt the coding sequences of exons.
Capping: In this process,an unusual nucleotide,$7$-methyl guanosine triphosphate,is added to the $5^{\prime}$-end of $hnRNA$.
Tailing: In this process,adenylate residues $(200-300)$ are added at the $3^{\prime}$-end of the transcript in a template-independent manner.