In a polymerase chain reaction, temperature required for the steps
(i) Denaturation,
(ii) Annealing and
(iii) Extension are respectively
A) ( i ) 94 ∘ C ( i i ) 40 ∘ C ( i i i ) 72 ∘ C
B) ( i ) 40 ∘ C ( i i ) 72 ∘ C ( i i i ) 94 ∘ C
C) ( i ) 94 ∘ C ( i i ) 72 ∘ C ( i i i ) 40 ∘ C
D) ( i ) 72 ∘ C ( i i ) 94 ∘ C ( i i i ) 40 ∘ C

Options

A. A) `(i) 94^(@)C (ii) 40^(@)C (iii) 72^(@)C`
B. B) `(i) 40^(@)C (ii) 72^(@)C (iii) 94^(@)C`
C. C) `(i) 94^(@)C (ii) 72^(@)C (iii) 40^(@)C`
D. D) `(i) 72^(@)C (ii) 94^(@)C (iii) 40^(@)C`

Answer

To solve the question regarding the temperatures required for the steps in a polymerase chain reaction (PCR), we will analyze each step of the PCR process and identify the correct temperatures associated with them.

### Step-by-step Solution:

1. **Identify the Steps of PCR**:
- The three main steps in PCR are:
- Denaturation
- Annealing
- Extension (or Elongation)

2. **Determine the Temperature for Denaturation**:
- During the denaturation step, the double-stranded DNA is heated to separate it into two single strands.
- The typical temperature for denaturation is **94°C**.

3. **Determine the Temperature for Annealing**:
- In the annealing step, short DNA primers bind to the single-stranded DNA templates.
- The temperature for annealing is generally lower than that of denaturation and typically falls within the range of **40°C to 60°C**. For this question, we can take **40°C** as a representative value.

4. **Determine the Temperature for Extension**:
- In the extension step, DNA polymerase synthesizes new DNA strands by adding nucleotides to the primers.
- The optimal temperature for this step is around **72°C**.

5. **Compile the Temperatures**:
- Now we have the temperatures for each step:
- Denaturation: **94°C**
- Annealing: **40°C**
- Extension: **72°C**

6. **Match with the Given Options**:
- We need to find the option that matches the temperatures we have identified:
- A) (i) 94°C (ii) 40°C (iii) 72°C
- B) (i) 40°C (ii) 72°C (iii) 94°C
- C) (i) 94°C (ii) 72°C (iii) 40°C
- D) (i) 72°C (ii) 94°C (iii) 40°C
- The correct option that matches our findings is **A**: (i) 94°C (ii) 40°C (iii) 72°C.

### Final Answer:
The correct answer is **A) (i) 94°C (ii) 40°C (iii) 72°C**.