Identify the gene which is not effective against cotton boll worms?

The correct answer is Option (1) → cryIAb

Option (1) cryIAb — Not effective against cotton bollworms. The protein of cryIAb controls the corn borer.

Option (2) cryIAc — Effective against cotton bollworms.

Option (3) cryIIAb — Effective against cotton bollworms.

Option (4) Both (2) and (3) — Both genes are effective against cotton bollworms. So this choice does not name a gene that is not effective.

NCERT Extract:
Biotechnological Applications in Agriculture – “… Specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into the several crop plants such as cotton (Figure 10.1). The choice of genes depends upon the crop and the targeted pest, as most Bt toxins are insect-group specific. The toxin is coded by a gene cryIAc named cry. There are a number of them, for example, the proteins encoded by the genes cryIAc and cryIIAb control the cotton bollworms, that of cryIAb controls corn borer.”