In the context of the developments in Bioinformatics, the term ‘transcriptome’, sometimes seen in the news, refers to

The transcriptome is the complete set of RNA transcripts produced by the genome of a cell, tissue or organism at a given time. In practice, aspirants mostly think of the mRNA fraction, which is what the term usually refers to in bioinformatics. So option B is correct.

Why the others fail:

• A) Enzymes used in genome editing, such as CRISPR-Cas9 nucleases, zinc-finger nucleases or TALENs, form the editing toolkit. That is a separate idea and is not what 'transcriptome' means.
• C) Describing the mechanism of gene expression is the job of molecular biology and regulation studies. It is not a dataset or a 'full set of molecules'.
• D) Genetic mutations arise through replication errors, DNA damage and mutagens. The transcriptome is not a mutation mechanism.

The core concept is the parallel between genome (all DNA), transcriptome (all RNA), and proteome (all proteins). Transcriptomics, using RNA-seq and microarrays, shows which genes are active under particular conditions. This links to Science and Technology and to Mains questions on biotechnology applications in health and agriculture.

Trap: aspirants pick A because genome editing is the buzzword in the news. Remember the '-ome' suffix family: genome (DNA), transcriptome (RNA), proteome (proteins).