A nucleoside is formed of

Options

A. Pentose sugar, phosphate and nitrogen base
B. Phosphate and nitrogen base
C. Pentose sugar and phosphate
D. Pentose sugar and nitrogen base.

Answer

To answer the question, "A nucleoside is formed of:", we need to analyze the components that make up a nucleoside.

### Step-by-Step Solution:

1. **Understanding Nucleosides**:
- A nucleoside is a basic structural unit of nucleic acids. It consists of two main components: a nitrogenous base and a sugar.

2. **Identifying the Components**:
- The nitrogenous base can be one of five types: adenine, guanine, cytosine, thymine (in DNA), or uracil (in RNA).
- The sugar component of a nucleoside is a pentose sugar, which can either be ribose (in RNA) or deoxyribose (in DNA).

3. **Eliminating Incorrect Options**:
- The options provided are:
- A) Pentose sugar, phosphate, and nitrogenous base
- B) Phosphate and nitrogenous base
- C) Pentose sugar and phosphate
- D) Pentose sugar and nitrogenous base
- Option A includes phosphate, which is not part of a nucleoside; it is part of a nucleotide.
- Option B also includes phosphate, which is incorrect for a nucleoside.
- Option C includes phosphate, which again is not part of a nucleoside.
- Option D includes only pentose sugar and nitrogenous base, which is correct.

4. **Conclusion**:
- Therefore, the correct answer is that a nucleoside is formed of **pentose sugar and nitrogenous base**.

### Final Answer:
A nucleoside is formed of **pentose sugar and nitrogenous base**.

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