Which of the following statements is incorrect?

The correct answer is Option (2) → pBR322 is a cloning vector of Salmonella typhimurium.

pBR322 is the cloning vector of E. coli. Salmonella typhimurium comes into the story elsewhere: the first recombinant DNA was made by linking an antibiotic resistance gene with a native plasmid of this bacterium.

Option (1) In micro-injection, recombinant DNA is directly injected into the nucleus of an animal cell. — A correct statement. Micro-injection puts recombinant DNA directly into the nucleus of an animal cell.

Option (2) pBR322 is a cloning vector of Salmonella typhimurium. — An incorrect statement. The book calls pBR322 an E. coli cloning vector, so linking it to Salmonella typhimurium is wrong.

Option (3) Agarose is a natural polymer extracted from sea weeds. — A correct statement. Agarose, the matrix used in gel electrophoresis, is a natural polymer obtained from sea weeds.

Option (4) Bacteriophages have very high copy numbers of their genome within bacterial cells. — A correct statement. Because bacteriophages are present in high numbers in each cell, the copy number of their genome in the bacterium is very high.

NCERT Extract:
Cloning Vectors – “You know that plasmids and bacteriophages have the ability to replicate within bacterial cells independent of the control of chromosomal DNA. Bacteriophages because of their high number per cell, have very high copy numbers of their genome within the bacterial cells.”
Figure 9.4 – “E. coli cloning vector pBR322 showing restriction sites (Hind III, EcoR I, BamH I, Sal I, Pvu II, Pst I, Cla I), ori and antibiotic resistance genes (amp^R and tet^R).”
Restriction Enzymes – “… Nowadays the most commonly used matrix is agarose which is a natural polymer extracted from sea weeds.”
Competent Host (For Transformation with Recombinant DNA) – “… In a method known as micro-injection, recombinant DNA is directly injected into the nucleus of an animal cell.”