Apopular classroom demonstration is to place a gas can on a burner and boil water in it. left unchecked this has the potential to be a very boring demo. however the can is removed from the flame and the lid is screwed on tightly. after it cools down the can will
a) still be boring and not change.
b) shrivel up, since colder gases have less pressure.
c) bulge and expand, since colder gases are denser and exert more pressure
d) shrivel up, since the atmosphere exerts more force on the can as it cools.

D) shrivel up, since the atmosphere exerts more force on the can as it cools.

Explanation:

As the water in the can is boiled the can gets heated up and contains hot vapour and gases which are rare in density and are in their expanded state. In this state when the can is sealed tightly such that no air leaks in or out of the can. When the temperature of the can drops, the gases shrink in volume and the pressure inside the can become less than the pressure of the atmosphere which leads to shriveling of the can.

d) physical means can be used to separate the components of air.