You place an empty one-gallon aluminum can in the unheated cargo compartment of your aircraft. just before closing the compartment, you place an airtight seal on the can. after takeoff, you climb from sea level to 10,000 feet msl for the cruise portion of your flight. your aircraft is unpressurized. what happens to the can? and why?

The can will remain the same.

Explanation:

Even the atmospheric pressure is different from sea level than a 10 000 feet MSL. Remember the second one has less atmospheric pressure because of the height, the column of air is smaller, so it produces less air pressure.

If the can is completely seal, even the atmospheric pressure inside will be more than the atmospheric pressure in the airplane. the can will remain the same, without bumps. But if is not seal, it will bump and maybe will explode because there is exchange in pressure.