To solve this problem, we need to understand the steps involved in the PCR process and identify which step is affected by temperature changes.$\newline$PCR, or Polymerase Chain Reaction, involves three main steps:$\newline \bullet$Denaturation:$\newline$ - This step involves heating the reaction mixture to a high temperature (usually around 94-98°C) to separate the double-stranded DNA into single strands.$\newline$ - This is the first step in the PCR cycle and is crucial for the subsequent steps.$\newline \bullet$Annealing:$\newline$ - After denaturation, the temperature is lowered (usually to 50-65°C) to allow primers to bind or anneal to the single-stranded DNA.$\newline \bullet$Extension:$\newline$ - The temperature is then raised to around 72°C, which is optimal for the DNA polymerase to extend the primers and synthesize new DNA strands.$\newline$If a very high temperature is not maintained in the beginning, the denaturation step will be affected first.$\newline$Without proper denaturation, the DNA strands will not separate, preventing the primers from annealing and the polymerase from extending the DNA.$\newline$Therefore, the correct option is Option 3: Denaturation.