A heterogeneous mixture is

Options

A. blood
B. air
C. vinegar
D. brass

Explanation

### Step-by-Step Solution:

1. **Understanding Heterogeneous Mixtures**:
- A heterogeneous mixture is defined as a combination of two or more substances that do not have a uniform composition. In these mixtures, the different components can be easily identified and separated.

2. **Characteristics of Heterogeneous Mixtures**:
- The components in a heterogeneous mixture can be physically separated. This means that you can distinguish and extract the individual substances without the need for chemical reactions.

3. **Examples of Heterogeneous Mixtures**:
- An example of a heterogeneous mixture is blood. Blood consists of various components such as red blood cells, white blood cells, and plasma. These components can be separated from each other physically.

4. **Comparison with Homogeneous Mixtures**:
- In contrast, homogeneous mixtures have a uniform composition throughout. For example, air is a homogeneous mixture because it contains gases that are evenly distributed. Similarly, vinegar, which is a solution of water and acetic acid, also has a uniform composition.

5. **Conclusion**:
- Among the given examples, blood is identified as a heterogeneous mixture because it contains different components that can be physically separated.