For a common person pure means having no adulteration. But, for a scientist all these things are actually mixtures of different substances and hence it is not pure.
Example: Milk is actually a mixture of water, fat, proteins etc.
A pure substance consists of a single type of particles. A substance is pure single form of the matter.
In the view of scientist “When all the constituent particles of a substance are the same in their chemical nature, it is known as pure substance“.
2.1 What is Mixture
The mixtures are constituted by more than one kind of pure form of matter.
By the physical process of evaporation we can separate dissolved sodium chloride from water.
Sugar contains only one kind of pure matter and its composition id the same throughout.
Soft drink and soil are not single pure substance.
Conclusion: A mixture contains more than one pure substance.