Phosphorus is a constituent of:

Options

A. fat
B. proteins
C. Nucleotides
D. carbohydrates

Answer

### Step-by-Step Solution:

1. **Understanding Phosphorus**: Phosphorus is an essential element found in various biological molecules. It plays a crucial role in several biochemical processes.

2. **Identifying Biological Molecules**: The question asks for the constituents of phosphorus. We need to identify which biological molecules contain phosphorus.

3. **Analyzing Nucleotides**: Nucleotides are the building blocks of nucleic acids (DNA and RNA). A nucleotide consists of three components: a sugar (ribose or deoxyribose), a phosphate group, and a nitrogenous base. Since nucleotides contain phosphate groups, they are indeed a constituent of phosphorus.

4. **Considering Proteins**: While some proteins may contain phosphorus (like phosphoproteins), not all proteins do. Therefore, it cannot be universally stated that proteins are a constituent of phosphorus.

5. **Examining Fats**: Fats (lipids) generally do not contain phosphorus. They are primarily made up of fatty acids and glycerol.

6. **Looking at Carbohydrates**: Carbohydrates are composed of carbon, hydrogen, and oxygen, and do not typically contain phosphorus.

7. **Conclusion**: Based on the analysis, the only biological molecule that is a clear and consistent constituent of phosphorus is nucleotides.

8. **Final Answer**: Phosphorus is a constituent of nucleotides.