A nucleoside lacks:

Options

A. phosphate group
B. sugar
C. base
D. hydroxyl group

Explanation

To solve the question "A nucleoside lacks:", we need to understand the structure of a nucleoside and how it differs from a nucleotide.

### Step-by-Step Solution:

1. **Definition of Nucleoside**: A nucleoside is a compound that consists of a nitrogenous base (which can be either a purine or a pyrimidine) attached to a five-carbon sugar (ribose or deoxyribose).

2. **Components of Nucleoside**:
- **Nitrogenous Base**: This can be adenine, guanine, cytosine, thymine, or uracil.
- **Five-Carbon Sugar**: This can be either ribose (in RNA) or deoxyribose (in DNA).

3. **Comparison with Nucleotide**: A nucleotide is similar to a nucleoside but includes one additional component: a phosphate group. Therefore, the main distinction is that nucleotides have a phosphate group, while nucleosides do not.

4. **Identifying the Lack**: Since we are asked what a nucleoside lacks, we can conclude that it lacks the phosphate group, which is present in nucleotides.

5. **Final Answer**: The correct answer to the question "A nucleoside lacks:" is the phosphate group.

### Conclusion:
The answer is **A. Phosphate group**.

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