The thermostable the enzyme used in PCR is :

The correct answer is Option (1) → Taq polymerase

Option (1) Taq polymerase — Correct. It comes from Thermus aquaticus and stays active through the heating steps.

Option (2) Exonuclease — Incorrect. An exonuclease removes nucleotides from the ends of DNA. PCR needs an enzyme that builds DNA, not one that breaks it.

Option (3) RNA polymerase — Incorrect. RNA polymerase makes RNA in transcription; PCR copies DNA.

Option (4) Endonuclease — Incorrect. An endonuclease cuts DNA at positions within it, such as restriction enzymes do.

NCERT Extract:
Amplification of Gene of Interest Using PCR – “… If the process of replication of DNA is repeated many times, the segment of DNA can be amplified to approximately billion times, i.e., 1 billion copies are made. Such repeated amplification is achieved by the use of a thermostable DNA polymerase (isolated from a bacterium, Thermus aquaticus), which remain active during the high temperature induced denaturation of double stranded DNA.”