A solution is a homogeneous mixture of two or more substances. Which of the following is a solution?

Options

A. milk
B. smoke
C. Brass
D. face cream

Answer

To determine which of the given options is a solution, we need to understand the definition of a solution and analyze the characteristics of each option.

### Step-by-Step Solution:

1. **Understanding the Definition of a Solution**:
- A solution is defined as a homogeneous mixture of two or more substances. This means that the components are uniformly distributed and cannot be easily separated by physical means.

2. **Analyzing the Options**:
- We need to evaluate each option provided to see if it meets the criteria of a solution.

3. **Option 1: Milk**:
- Milk is a colloidal mixture where fat droplets are dispersed in water. Since it does not have a uniform composition throughout, it is not considered a solution.

4. **Option 2: Smoke**:
- Smoke is a colloid consisting of solid particles dispersed in a gas. Similar to milk, it is not homogeneous at a microscopic level, so it cannot be classified as a solution.

5. **Option 3: Brass**:
- Brass is an alloy made of copper and zinc. It is a solid-solid solution where the two metals are mixed uniformly at the atomic level. This meets the definition of a solution.

6. **Option 4: Face Cream**:
- Face cream is an emulsion, which is a type of colloidal mixture. It consists of fat droplets dispersed in water, and like milk, it is not a homogeneous solution.

7. **Conclusion**:
- Among the options analyzed, brass is the only one that qualifies as a solution because it is a homogeneous mixture of two metals.

### Final Answer:
Brass is a solution.