Question

Two similar chemicals, one with higher molecular mass than the other. Which one will sublime first in fractional sumblimation?

Answer 1

It says two similar chemicals so we can assume they have similar bonding. If we take the example of Iodine it sublimes  because of the relatively weak Van der Waals forces holding the I2 molecules together. Iodine has a very high molecular mass (over 200 grams per mole) so the high mass of the molecule causes it to remain as a solid at room temperature. However, the overall forces holding it together are very weak so if it gets enough energy to break free from itself, it forms a vapor right away instead of a liquid.

So the higher molecular mass solid will sublime first.