With respect to Chargaff's rule, select the option that shows appropriate base pairing.

Options

A. AG, CT
B. AC, GT
C. AT, GC
D. All of these

Answer

To solve the question regarding Chargaff's rule and appropriate base pairing, we will follow these steps:

### Step 1: Understand Chargaff's Rule
Chargaff's rule states that in double-stranded DNA, the amount of adenine (A) is equal to thymine (T), and the amount of guanine (G) is equal to cytosine (C). This means:
- A = T
- G = C

### Step 2: Identify Nitrogenous Bases
The nitrogenous bases in DNA are divided into two categories:
- Purines: Adenine (A) and Guanine (G)
- Pyrimidines: Cytosine (C) and Thymine (T)

### Step 3: Analyze the Given Options
The options provided are:
1. AG, CT
2. AC, GT
3. AT, GC
4. All of these

Now we will analyze each option based on Chargaff's rule.

### Step 4: Evaluate Each Option
1. **AG, CT**: This pairing does not follow Chargaff's rule as A does not pair with G, and C does not pair with T.

2. **AC, GT**: This pairing also does not follow Chargaff's rule as A does not pair with C, and G does not pair with T.

3. **AT, GC**: This pairing follows Chargaff's rule as A pairs with T and G pairs with C.

4. **All of these**: This option cannot be correct since only one of the previous options follows Chargaff's rule.

### Step 5: Conclusion
The correct answer is option **3: AT and GC**, as it represents the appropriate base pairing according to Chargaff's rule.

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