Which one of the following is not a mixture?

Options

A. Brass
B. Air
C. 22 carat gold
D. Water

Answer

To determine which of the following options is not a mixture, we need to analyze each option provided:

1. **Brass**: Brass is an alloy composed of copper and zinc. Since it is made up of two or more elements combined physically, it is a mixture.

2. **Air**: Air is a mixture of various gases, including nitrogen, oxygen, carbon dioxide, and water vapor. Therefore, air is also a mixture.

3. **22 Carat Gold**: This is an alloy that consists of 92% gold and 8% other metals (like silver, zinc, and nickel). Since it contains more than one type of element, it is considered a mixture.

4. **Water (H2O)**: Water is a chemical compound formed from the chemical combination of hydrogen and oxygen in a fixed ratio. It does not consist of multiple components mixed together; rather, it is a pure substance.

Based on this analysis, the answer is:

**Water is not a mixture; it is a compound.**

### Step-by-Step Solution:
1. **Identify Each Substance**: List the substances provided (Brass, Air, 22 Carat Gold, Water).
2. **Determine Composition**: Analyze the composition of each substance:
- Brass: Mixture of copper and zinc.
- Air: Mixture of gases (nitrogen, oxygen, etc.).
- 22 Carat Gold: Mixture of gold and other metals.
- Water: Chemical compound of hydrogen and oxygen.
3. **Classify Each Substance**: Classify them as either a mixture or a pure substance:
- Brass: Mixture
- Air: Mixture
- 22 Carat Gold: Mixture
- Water: Pure substance (compound)
4. **Conclude**: Identify which substance is not a mixture. In this case, it is water.