Milk is not considered a pure substance. A pure substance is a material that has a constant composition and consistent properties throughout the sample. Examples of pure substances include elements like gold and compounds like water.
Milk, on the other hand, is a complex mixture of various components. It contains water, fats, proteins, lactose (milk sugar), minerals, and vitamins. These components are not chemically bonded to each other, and their proportions can vary depending on the source of the milk and its processing.
Because milk is a mixture of different substances, it does not have a fixed composition or consistent properties. Therefore, milk is classified as a mixture rather than a pure substance.