Chargaff's rules of base pairing is applicable for

Options

A. Single stranded DNA
B. Double stranded DNA
C. Single stranded RNA
D. All except (3)

Answer

To solve the question regarding Chargaff's rules of base pairing, we need to analyze the options provided and understand the context of Chargaff's rules.

### Step-by-Step Solution:

1. **Understanding Chargaff's Rules**: Chargaff's rules state that in a double-stranded DNA molecule, the amount of adenine (A) is equal to the amount of thymine (T), and the amount of cytosine (C) is equal to the amount of guanine (G). This is due to the specific base pairing that occurs: A pairs with T and C pairs with G.

2. **Identifying the Type of Nucleic Acid**: The question asks for which type of nucleic acid Chargaff's rules apply. The options given are:
- Single-stranded DNA
- Double-stranded DNA
- Single-stranded RNA
- All except three

3. **Analyzing Each Option**:
- **Single-stranded DNA**: Chargaff's rules do not apply because there is no complementary strand for base pairing.
- **Double-stranded DNA**: Chargaff's rules apply here as base pairing occurs between the two strands.
- **Single-stranded RNA**: Chargaff's rules do not apply because, similar to single-stranded DNA, there is no complementary strand for base pairing.
- **All except three**: This option implies that Chargaff's rules apply to some but not all of the given types, which is misleading since they specifically apply to double-stranded DNA only.

4. **Conclusion**: Based on the analysis, Chargaff's rules of base pairing are applicable only to double-stranded DNA.

### Final Answer:
The correct answer is **double-stranded DNA**.

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