About Science

It all depends on the relative density of the liquid/gas in the medium.

For example:

Petroleum gas (石油氣) in air will go "down". So in case of 漏石油氣...don't claw on the floor because the "gas" will sink and concentrate on the floor, if you stay on the floor, you will suffucate.

Petroleum(oil - liquid) in water will go "up" to the top. So if oil leakage from a boat/ship at sea, don't swim directly near the boat/ship becaue the oil may be on fire or seal the surface of the water that you'll just cover by oil. Swim away from the "spill" before surfacing.

So the movement depends on the medium the "liquid"/"gas" is in.

If in the same temperature and in the same medium, I think liquid will move faster than gas.

It depends on the density of the gas of liquid.

Carbon dioxide sinks because it is denser than air.

這要看相對密度而定，水份可上浮，揮發汽油下沉，不同密度不能比，快慢無意義。