Chemically an antibody is

Options

A. Protein
B. Lipid
C. Lipoprotein
D. Nucleoprotein

Answer

### Step-by-Step Solution:

1. **Understanding Antibodies**: Antibodies are specialized proteins produced by the immune system in response to antigens, which are foreign substances that enter the body.

2. **Chemical Nature of Antibodies**: The primary chemical nature of antibodies is that they are proteins. This means they are made up of long chains of amino acids.

3. **Structure of Antibodies**: Antibodies consist of two pairs of polypeptide chains: one pair is known as heavy chains and the other as light chains. This structure is crucial for their function in the immune response.

4. **Function of Antibodies**: Antibodies bind to specific antigens, neutralizing their effects and marking them for destruction by other immune cells.

5. **Evaluating Options**:
- Option 1: Protein - This is correct as antibodies are indeed proteins.
- Option 2: Lipid - Incorrect, as antibodies are not lipids.
- Option 3: Lipoprotein - Incorrect, as this term refers to a combination of lipids and proteins, which does not apply to antibodies.
- Option 4: Nucleoprotein - Incorrect, as this term refers to proteins associated with nucleic acids, which does not apply to antibodies.

6. **Conclusion**: The correct answer is that antibodies are proteins in nature.

### Final Answer:
**Chemically, an antibody is a protein.**

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