The cooling curve above shows how the temperature of a sample varies with time as the sample goes through phase changes. the sample starts as a gas, and heat is removed at a constant rate. at which time does the sample contain the most liquid?

float.

archimedes' principle

denser than water sinks in water.

denser than mercury would sink in it

3. dark matter

empty space could also be a simple vacuum

one "light year" is the distance that light travels, through vacuum, in one julian year.   that's 365.25 days, of 24 hours each.