What helps in identifying and eliminating non-transformants?

The correct answer is Option (1) → Selectable marker

Option (1) Selectable marker — Correct. A selectable marker is a gene, usually one giving resistance to an antibiotic, that lets us pick out the transformed cells. On a medium with that antibiotic the non-transformants die, so they are identified and removed.

NCERT Extract:
Cloning Vectors – “… (ii) Selectable marker : In addition to ‘ori’, the vector requires a selectable marker, which helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants. Normally, the genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for E. coli.”