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

In the above question we noticed that there is a passage from a regular and well compacted carbon dioxide molecules to molecules in a less compact and lower density pattern after a period of heating. According to this description we can conclude that a physical process called "Melting" occurred, which is the process, where a solid substance (which has very compacted molecules) when heated becomes a liquid substance, with less compacted molecules and lower density.

Melting explains the changeover from heating to solid state to liquid state. Heating causes the temperature of the substance to rise to its melting point. The temperature does not rise while fusion is taking place, that is, only after all the substance has gone into liquid state does the temperature rise again.

The melting point of a substance is the temperature at which that substance changes from solid to liquid state.