What is the half-life of an isotope if 200 g is left from an 800 g original sample of the isotope remains after 4.0 years ?

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