<span>The outer layers of the planet are gas. Deeper within the planet, pressure compresses the gases into a liquid. Some evidence suggests that Jupiter may have a small rocky core at its center.</span>
We can explain this in a molecular level. We know that the difference between a gas and a liquid of the same composition is how fast their molecules are moving. So given a gas, their molecules are farther and faster when moving, but when they are cooled their bulk kinetic energy decreases. In other words their molecules start to move closer and move slower until it behaves more like a liquid molecule. This is the time when gases condense.
A) Head to tail joining of monomers. :) (confirmed correct answer, I took the test)
