Which among the following is an element?

Options

A. Calcium oxide
B. Common salt
C. Ozone
D. Water

Explanation

To determine which among the given options is an element, we can follow these steps:

### Step 1: Understand what an element is
An element is a pure substance that consists of only one type of atom. Elements cannot be broken down into simpler substances by chemical means.

### Step 2: Analyze the options
We need to look at each option provided and identify if it consists of only one type of atom.

1. **Calcium Oxide (CaO)**:
- This compound consists of calcium (Ca) and oxygen (O). Since it contains more than one type of atom, it is not an element.

2. **Common Salt (NaCl)**:
- Common salt is made up of sodium (Na) and chlorine (Cl). Again, it has more than one type of atom, so it is not an element.

3. **Ozone (O3)**:
- Ozone consists of three oxygen atoms. Since it is made up of only one type of atom (oxygen), it qualifies as an element.

4. **Water (H2O)**:
- Water is composed of hydrogen (H) and oxygen (O). It contains more than one type of atom, so it is not an element.

### Step 3: Conclusion
Among the options analyzed, the only substance that is an element is **Ozone (O3)**.

### Final Answer
The correct answer is **Ozone (O3)**.

---