What is the largest (size) solid object ever dropped from an airplane to impact the ground in freefall? What is the record for the largest single solid item that has ever been dropped from an airplane at free fall to the ground? 


Here, "free fall" means falling vertically, or nearly vertically falling allowing some leeway for expected horizontal movement such as the ground speed of the plane doing the drop, winds, or unintended Magnus effect among other things, and allows for normal atmospheric air resistance.
The object being dropped should be payload, not part of the vehicle doing the dropping.
The object should not be designed with the intent to generate lift. For example, the above mentioned Magnus effect would disqualify if a machine was purposely built to spin with the intention of generating lift. This includes things with wings, parachutes, landing thrusters, etc.
The object must have hit the ground in an uncontrolled descent in the past. In other words, satellites in free-fall orbit around the Earth do not count unless they fell to the ground and then got re-launched into orbit again (unlikely).
Objects that burn up in the atmosphere do not reach the ground as a single solid object, so they do not count unless any possibly remaining fragment that may reach the ground is still the biggest object to be dropped and reach the ground in its destroyed state (unlikely).
The item does not have to have been intentionally dropped. For example, if it were dropped with a parachute, but the parachute failed to deploy, that counts.
Bombs easily count as long as they don't have a parachute, thrusters, wings or any other design factor that is intended to generate lift.
Last, but not least, "largest" means greatest volume, not heaviest.
I can't think of anything dropped from an aircraft larger than the US Space Shuttle when it was dropped from a specially modified 747 during the testing phases of development.