It could sink. (The metal's density is greater than water.) It could turn into a ball of flames. (If you dropped a chunk of sodium into graduated cylinder, it would react with flames or sparks.)
Filled with air
Helium is lighter than air and a balloon filled with helium may rise up.
it would expand
Nothing will happen as neon is chemically inert due to the presence of completely filled orbitals.
Not the sun specifically, but a partial supernova was recently found to occasionally happen in two-star systems. See the related link below.
it hurts
If it is a water-filled or oil-filled radiator, it will leak fluid.
One would float atop the other. Oil and water do not mix at the particle level because those substances possess different intermolecular forces between their particles.
Autolyzing means self digesting. A partially autolyzed brain is one who is partially self digesting. This can happen postmortem (McCance, Huether, 3rd Ed. Understanding Pathophysiology)
the air would be trapped in the measuring cylinder. basically, nothing would happen
Nothing will happen. Nothing will happen. I think.
Filled with air
Putting an air-filled balloon in a refrigerator will cause it to shrink.
That is partially true, some incidents happen with misusing the Fireplace.
You would cough or choke
The water in it would heat up, and partially evaporate.
there would be loots of wood