RNAi takes place in all eukaryotic organisms as a method of

The correct answer is Option (3) → cellular defense

Option (3) cellular defense — Correct. Of the options, only cellular defense is the role NCERT gives to RNA interference (RNAi) in eukaryotes.

Note: A similar question was also asked in CUET (UG) 2023 on 11-06-2023 (Slot 3).

NCERT Extract:
Biotechnological Applications in Agriculture – “… Pest Resistant Plants: Several nematodes parasitise a wide variety of plants and animals including human beings. A nematode Meloidegyne incognitia infects the roots of tobacco plants and causes a great reduction in yield. A novel strategy was adopted to prevent this infestation which was based on the process of RNA interference (RNAi). RNAi takes place in all eukaryotic organisms as a method of cellular defense.”