Final answer:
The answer to which example is a mixture is d) Air, as it is a homogeneous mixture of various gases like nitrogen, oxygen, and carbon dioxide.
Step-by-step explanation:
The question is asking to identify which of the given examples is a mixture. Mixtures are combinations of two or more pure substances in which the individual substances retain their identity. Examples of mixtures include stews, seawater, and notably, air. Based on the information provided, we know that air is composed of a combination of gases such as nitrogen, oxygen, carbon dioxide, and others, making it a homogeneous mixture because it has a uniform composition throughout. Therefore, the answer to the question is d) Air, which is a mixture of different gases.