Potential energy increases and an objects increases ? ? !

I think the answer is speed:

The following equation is used to represent the kinetic energy (KE) of an object. This equation reveals that the kinetic energy of an object is directly proportional to the square of its speed. That means that for a twofold increase in speed, the kinetic energy will increase by a factor of four.

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