What are the mobile genetic elements called?

The correct answer is Option (1) → Transposons

Transposons are mobile genetic elements: pieces of DNA that can move from one place to another in the genome. Some transposons replicate through an RNA intermediate. Such RNA, like the RNA of viruses with RNA genomes, can be a source of the double-stranded RNA that starts RNA interference (RNAi), a natural defence of eukaryotic cells. Introns, promoters and cistrons do not move: introns are the non-coding sequences removed from hnRNA during splicing, a promoter is the site where RNA polymerase binds to start transcription, and a cistron is a segment of DNA coding for a polypeptide.

NCERT Extract:
Biotechnological Applications in Agriculture – “… RNAi takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA due to a complementary dsRNA molecule that binds to and prevents translation of the mRNA (silencing). The source of this complementary RNA could be from an infection by viruses having RNA genomes or mobile genetic elements (transposons) that replicate via an RNA intermediate.”