Which of the following statements are incorrect?(A) Fragments of DNA…

The correct answer is Option (1) → (A) and (C) only

(A) Fragments of DNA can be separated by ELISA. False. DNA fragments are separated by gel electrophoresis. Being negatively charged, they move through the agarose gel towards the anode, and the smaller ones move farther. ELISA is a diagnostic test based on antigen-antibody interaction.

(B) Transformation is a procedure through which a piece of DNA is introduced in a host bacterium. True. This is what transformation means. The bacterium that takes up the DNA is called a transformant.

(C) Recombinant DNA technology does not involve isolation of a desired DNA fragment. False. The technology begins with isolation of DNA. The DNA is then cut with restriction enzymes, the desired fragment is isolated and joined into a vector.

(D) DNA ligases are used for stitching DNA fragments into a vector. True. DNA ligase joins the cut ends, sealing the desired fragment into the vector.

NCERT Extract:
Separation and Isolation of DNA Fragments – “The cutting of DNA by restriction endonucleases results in the fragments of DNA. These fragments can be separated by a technique known as gel electrophoresis. Since DNA fragments are negatively charged molecules they can be separated by forcing them to move towards the anode under an electric field through a medium/matrix.”
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. Transformation is a procedure through which a piece of DNA is introduced in a host bacterium (you will study the process in subsequent section).”
Processes of Recombinant DNA Technology – “Recombinant DNA technology involves several steps in specific sequence such as isolation of DNA, fragmentation of DNA by restriction endonucleases, isolation of a desired DNA fragment, ligation of the DNA fragment into a vector, transferring the recombinant DNA into the host, culturing the host cells in a medium at large scale and extraction of the desired product.”