The kelvin temperature/scale i think
Galaxies are sprawling systems of dust, gas, dark matter, and anywhere from a million to a trillion stars that are held together by gravity. Nearly all large galaxies are thought to also contain supermassive black holes at their centers.
1)

<Solve using the formula which is:
Mass=Density×Volume

2)
3)

(Length × Width × Height)


(Answer=7.5)
I am not sure how you want me to answer this, but yes, gas can go from being a gas to a liquid when the right temp and pressure is applied.