A. a puck hovers and glides across an air track at constant velocity.

b. a dishwasher was pulled up to a window by a rope using a pulley system.

c. a feather falls from one end of a tube to the other inside a vacuum.

d. a charged particle was pushed away by another charged particle.

Option C

A feather falls from one end of a tube to the other inside a vacuum

Explanation:

In conservative force field, which in this case is a vacuum, you expect that there will be no loss of energy to air-friction. Therefore, when a feather falls from one end of the tube to the other side which is a vacuum, we expect no energy loss. Conservative forces are the forces that are path-independent. This implies that in a closed loop, the total work done is zero. Considering the options given, only feather falls from one end of a tube to the other inside a vacuum meets the criteria

heat the gas and measure the pressure

a lot of it means it can be "burned" for energy and sold at one price. if it is scarce, the price will go up