Which of the following statements is correct?

Options

A. A pure substance must contain only one type of atom.
B. A mixture containing two compounds must be heterogeneous.
C. A heterogeneous mixture must contain at least three elements.
D. A homogeneous mixture must be uniform.

Answer

To determine which statement is correct, we will analyze each option provided in the question step by step.

### Step 1: Understand the nature of elements
- **Statement Analysis**: Elements are pure substances that consist of only one type of atom. This means that if a substance contains only one kind of atom, it is classified as an element and is considered a pure substance.
- **Conclusion**: This statement is generally correct, but it does not imply that all substances with one atom are pure substances.

### Step 2: Analyze mixtures of compounds
- **Statement Analysis**: A mixture containing two compounds can be either homogeneous or heterogeneous. A homogeneous mixture has a uniform composition, while a heterogeneous mixture does not.
- **Conclusion**: This statement is false because a mixture of two compounds can be homogeneous.

### Step 3: Evaluate the requirement for a heterogeneous mixture
- **Statement Analysis**: A heterogeneous mixture does not need to contain at least three elements; it can consist of just two components (elements or compounds).
- **Conclusion**: This statement is false because a minimum of two components is sufficient to form a mixture.

### Step 4: Check the definition of a homogeneous mixture
- **Statement Analysis**: A homogeneous mixture must have a uniform composition throughout. This means that the components are evenly distributed and cannot be easily distinguished.
- **Conclusion**: This statement is true.

### Final Conclusion
After analyzing all the statements, the correct statement is: "A homogeneous mixture must be uniform."