If in double stranded DNA molecule, cytosine is 40%, then the percentage of adenine would be :-

Options

A. 0.6
B. 0.4
C. 0.2
D. 0.1

Answer

To solve the problem, we need to apply Chargaff's rules, which state that in a double-stranded DNA molecule, the amount of adenine (A) is equal to thymine (T), and the amount of guanine (G) is equal to cytosine (C).

### Step-by-step Solution:

1. **Identify the percentage of cytosine (C):**
- The problem states that cytosine is 40%.

2. **Apply Chargaff's rule for guanine (G):**
- According to Chargaff's rule, the percentage of guanine is equal to the percentage of cytosine. Therefore, if C = 40%, then G = 40% as well.

3. **Calculate the total percentage of C and G:**
- Add the percentages of cytosine and guanine:
\[ C + G = 40\% + 40\% = 80\% \]

4. **Determine the remaining percentage for adenine (A) and thymine (T):**
- Since the total percentage must equal 100%, we subtract the combined percentage of C and G from 100%:
\[ 100\% - 80\% = 20\% \]
- This means that the combined percentage of adenine and thymine is 20%.

5. **Apply Chargaff's rule for adenine (A) and thymine (T):**
- According to Chargaff's rule, the percentage of adenine is equal to the percentage of thymine (A = T). Therefore, if A + T = 20%, we can divide this by 2 to find the percentage of adenine:
\[ A = T = \frac{20\%}{2} = 10\% \]

6. **Convert the percentage of adenine into decimal form:**
- To express 10% in decimal form, we divide by 100:
\[ A = 10\% = 0.1 \]

7. **Conclusion:**
- The percentage of adenine in the double-stranded DNA molecule is 10%, which is represented as 0.1 in decimal form.

### Final Answer:
The percentage of adenine is **0.1**.

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