Which of the following samples of DNA in the table given below will give the desired result during polymerase chain reaction ?

The correct option is Sample - I: Temperature used for Denaturation - High temp. / 90° C, Enzyme used for extension - Heat stable.

To understand why this is the correct setup, let us break down the steps of the Polymerase Chain Reaction (PCR) and analyze the required conditions:
1. Denaturation Step:
During the denaturation step, the double-stranded DNA template must be separated into single strands by breaking the hydrogen bonds between the complementary bases. This process requires a high temperature, typically between 90° C and 95° C. A low temperature, such as 50° C (mentioned in Sample - II and Sample - III), is insufficient to separate the strands, preventing the reaction from starting.
2. Extension Step and Enzyme Requirement:
The enzyme responsible for extending the primers to synthesize new DNA strands is a DNA polymerase. Because the PCR cycle involves repeated heating steps to high temperatures (near 90° C–95° C), the DNA polymerase used must be heat-stable (thermostable), such as Taq polymerase. A heat-unstable enzyme (mentioned in Sample - IV) would denature and lose all catalytic activity during the first denaturation cycle, rendering the PCR inactive.

Therefore, only Sample - I provides both the necessary high denaturation temperature (90° C) to separate the template DNA strands and a heat-stable enzyme to withstand the thermal cycles and perform extension successfully.