Which one of the following is not an element ?

Options

A. Graphite
B. Water
C. Diamond
D. Nitrogen

Answer

To solve the question "Which one of the following is not an element?" we need to analyze each option provided: graphite, water, diamond, and nitrogen.

### Step-by-Step Solution:

1. **Understanding Elements**:
- An element is defined as a pure substance consisting of only one type of atom, which has the same number of protons in their atomic nuclei.

2. **Analyzing Graphite**:
- Graphite is a form of carbon. It consists solely of carbon atoms arranged in a hexagonal structure. Since it contains only one type of atom (carbon), graphite is classified as an element.

3. **Analyzing Water**:
- Water (H2O) is composed of two different elements: hydrogen and oxygen. Since it contains more than one type of atom, it is not a pure substance and is classified as a compound.

4. **Analyzing Diamond**:
- Diamond is another form of carbon. Like graphite, it consists only of carbon atoms, but they are arranged in a cubic structure. Therefore, diamond is also classified as an element.

5. **Analyzing Nitrogen**:
- Nitrogen is a diatomic molecule (N2) but consists solely of nitrogen atoms. Each nitrogen atom has the same number of protons (7), which qualifies nitrogen as an element.

6. **Conclusion**:
- Among the options provided, water is the only substance that is not an element. It is a compound formed from two different elements (hydrogen and oxygen).

### Final Answer:
The correct answer is **water**.

---