Which of the following is an element?

Options

A. air
B. hydrogen
C. water
D. carbon dioxide

Answer

To determine which of the following is an element among air, hydrogen, water, and carbon dioxide, 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 each option
- **Air**: Air is a mixture of different gases (like nitrogen, oxygen, carbon dioxide, etc.) and is not made up of only one type of atom. Therefore, air is not an element.

- **Hydrogen**: Hydrogen is a chemical element represented by the symbol 'H'. It consists of only hydrogen atoms. Therefore, hydrogen is an element.

- **Water**: Water (H₂O) is a compound made up of two hydrogen atoms and one oxygen atom. Since it contains more than one type of atom, water is not an element.

- **Carbon Dioxide**: Carbon dioxide (CO₂) is also a compound made up of one carbon atom and two oxygen atoms. Since it contains more than one type of atom, carbon dioxide is not an element.

### Step 3: Identify the correct answer
From the analysis, the only option that is an element is **hydrogen**.

### Conclusion
The correct answer is **hydrogen**.

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