Casein of milk is
(a) Glycoprotein
(b) Phosphoprotein
(c) Chromoprotein
(d) Metalloprotein

Options

A. Glycoprotein
B. Phosphoprotein
C. Chromoprotein
D. Metalloprotein

Answer

To determine the type of protein that casein of milk is, we can follow these steps:

### Step-by-Step Solution:

1. **Identify Casein**:
- Casein is a protein found in milk. It is one of the primary proteins in mammalian milk.

2. **Understand Protein Types**:
- There are different types of proteins, including glycoproteins, phosphoproteins, chromoproteins, and metalloproteins. Each type has specific characteristics:
- **Glycoproteins**: Proteins that have carbohydrate groups attached.
- **Phosphoproteins**: Proteins that contain phosphate groups.
- **Chromoproteins**: Proteins that contain a pigmented prosthetic group.
- **Metalloproteins**: Proteins that contain a metal ion as a cofactor.

3. **Research Casein Composition**:
- Casein is known to contain phosphate groups, which qualifies it as a phosphoprotein. It is a significant component of milk, making up about 80% of the total protein content in mammalian milk.

4. **Analyze the Options**:
- Given the definitions and the composition of casein, we can analyze the options:
- (a) Glycoprotein - Incorrect, as casein does not primarily contain carbohydrates.
- (b) Phosphoprotein - Correct, since casein contains phosphate groups.
- (c) Chromoprotein - Incorrect, as casein does not contain a pigmented prosthetic group.
- (d) Metalloprotein - Incorrect, as casein does not contain a metal ion.

5. **Conclusion**:
- Based on the analysis, the correct answer is (b) Phosphoprotein.

### Final Answer:
(b) Phosphoprotein