Answer the following question given this paragraph: 

In the previous lesson, we discussed pure substances and mixtures. We indicated that the components of a mixture could be separated by physical means, but the components of a pure substance could not. Pure substances can only be broken down further through chemical means. In this lesson, we list several methods for separating mixtures. We will also be looking at chemical changes which alter the chemical identity of a substance, and how to recognize when a chemical change is taking place.


Q: While components of a mixture can be separated by physical means, the components of a pure substance can only be broken down through what means?


A:
chemical