Yes
(Finish answer by saying why)
The gasses are compressed mainly so they can fit in a smaller space. If the gasses were not compressed it would be very inconvenient and costly to reserve the space for the quantities of gas needed.
Gunpowder, also compressed gasses and compressed air.
Yes, water vapor is a gas and all gasses can be compressed.
Yes gasses are compressible.
Yes, liquids can be compressed, but relatively little, and requiring much higher pressures compared to gasses.
Liquids CAN be compressed ... but not as much as gasses, nor as easily. The reason is that there is no "free space" between the molecules of a liquid (nor of a solid), but there is between the molecules of a gas.
solids cannot be compressed at all, if you compress a liquid enough it will become a solid by freezing, gasses can be compressed however if compressed enough it will become a liquid
Many gasses will turn to liquid when compressed, as in Propane, when compressed becomes liquid propane gas LPG
The same forced compression that is used for liquid propane, and all other compressed gasses
Because the gasses are compressed and cooled to -200 degress
DOT division 2.2 is for compressed nonflammable gasses.
Compressional, gasses can be compressed but cannot be wiggled side to side.