Salt water is classified as a
1) compound because the proportion of its atoms is fixed
2) compound because the proportion of its atoms can vary
3) mixture because the proportion of its components is fixed
4) mixture because the proportion of its components can vary

The following transition occurs at a molecular level for a substance. what transition corresponds to this change in microscopic structure? the carbon dioxide molecules on the left are in a regular, tightly packed pattern. after heating, it becomes much lower density. a. melting b. boiling c. sublimation d. freezing