1. Compressibility is the how much the volume of a gas can shrink under pressure. This affects the behavior of the gas by determining how tightly it can be packed.
2. A ballast tank in a submarine is used to make the submarine dive or rise. It changes the amount of water in it, which changes the density of the submarine, and can thus change the submarine’s density from positive to negative buoyancy or vice versa.
3. .161 atm
1. I was looking for something along the lines of "deviation of real gas behavior from ideal gas behavior," but I probably should've specified better, so sorry about that. When the compressibility factor deviates more from 1, the compressibility factor of an ideal gas, the gas acts less ideal and more like a real gas.
3. Correct (.2 atm for sig figs)