If a feather and an iron bar is released from a same height in a room without any air resistance, which one (s) will impact the ground first.

A) neither one, because without air resistance gravity is absent

B) iron bar

C) both

D) feather

If there is absolutely no resistance which can impede the flow or the drop of the feather and iron bar, therefore the only force that must be acting upon it is the force due to gravity. Since both objects are being accelerated by an amount of 9.81 m/s^2, therefore both objects will reach the ground together.

Hence the answer is:

C. both