Which of the following pairs is incorrectly matched?

Options

A. Purines - Adenine and Guanine
B. Pyrimidines - Cytosine and Uracil
C. Nucleosides - Adenosine and Thymidine
D. DNA-Polynucleoside

Answer

To determine which of the following pairs is incorrectly matched, we will analyze each pair one by one.

### Step 1: Analyze the first pair - Purines
- **Purines** are nitrogenous bases that include **adenine** and **guanine**.
- This pair is correctly matched.

### Step 2: Analyze the second pair - Pyrimidines
- **Pyrimidines** are another type of nitrogenous base that includes **cytosine** and **uracil**.
- This pair is also correctly matched.

### Step 3: Analyze the third pair - Nucleosides
- **Nucleosides** consist of a nitrogenous base and a sugar, without a phosphate group.
- **Adenosine** (adenine + sugar) and **thymidine** (thymine + sugar) are both examples of nucleosides.
- This pair is correctly matched.

### Step 4: Analyze the fourth pair - DNA
- DNA is a **polynucleotide**, which means it is made up of multiple nucleotides.
- A nucleotide consists of a nitrogenous base, a sugar, and a phosphate group.
- The term **polynucleoside** is incorrect because it does not account for the phosphate group present in nucleotides.
- Therefore, this pair is incorrectly matched.

### Conclusion
The incorrectly matched pair is the fourth option: "DNA is a polynucleoside."

### Final Answer
The answer is option number 4.

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