Question

How can a homogenous mixture not be called a pure substance?

Answer 1

A pure substance is an individual entity whose elements can not be separated further. It has fixed chemical composition and may occur in any of the state i.e solid,liquid or gaseous.Therefore pure substance can not be separated by any physical of chemical methods.
Whereas Mixture is combination of two or more substance and thus its elements can be separated. The components of Homogeneous mixture can be separated by physical or chemical methods. Homogeneous mixture is a physical combination of substances in which pure substances retain their chemical properties.