Convection currents form when warm air rises and cold air sinks. What causes the warm air to rise and the cold air to sink? A. chemical energy B. activation energy O C. a difference in density D. the law of conservation

the answer is C difference in density because hot air is less dense than cold air so hot air will rise and cold air will fall.

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.