Question

what is the main difference between a pure substance and a mixture? mixtures are always liquids; pure substances are always solids. pure substances have a fixed composition; mixtures do not. pure substances can be separated by physical means; mixtures cannot. mixtures have a fixed composition; pure substances do not.

Explanation:

A pure substance has a definite and constant composition. Mixtures have variable compositions as they are made up of two or more substances physically combined. Physical - separation methods are for mixtures, not pure substances. Also, pure substances and mixtures can exist in all states of matter.

Answer:

B. Pure substances have a fixed composition; mixtures do not.