Which of the following options correctly ranks solid iodine, liquid bromine and chlorine gas in the order of increasing intermolecular force strength? a
liquid bromine < solid iodine < chlorine gas
b
solid iodine < chlorine gas < liquid bromine
c
solid iodine < liquid bromine < chlorine gas
d
chlorine gas < liquid bromine < solid iodine

B. solid iodine <chlorine gas

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.