Final answer:
Oxygen is not a mixture because it is an element. Salad, sea water, and Pepsi are examples of mixtures.
Step-by-step explanation:
Oxygen is not a mixture. It is an element that exists as a pure substance. A mixture is a combination of two or more substances that are physically combined. Salad, sea water, and Pepsi are all examples of mixtures because they are made up of different substances that can be separated physically.
Learn more about Differentiating mixtures and pure substances