A pure substance is different from a mixture because D. mixtures can be separated by physical means. You can eliminate all of the other answers to find this out. A is incorrect because a pure substance is just that, a pure substance, while a mixture is multiple substances. B is incorrect because a pure substance is one substance, while heterogeneous is a type of mixture, which has multiple substances. And C is incorrect because a mixture is a blend of 2 or more substances.
