The surface of planet Earth is made up of 71% water.
Earth is covered mostly in water, but is not made up mostly of water. Most of earth is made of rock.
Earth is the planet that is mostly made of liquid water, covering approximately 71% of its surface.
Earth.
Pluto is probably nearly 50% water ice. Of course, it was demoted to "dwarf planet" status.
Mercury is a rocky planet.
Mars is known as the red planet. The planet itself is mostly rock. It is the thin atmosphere that is mostly carbon dioxide.
Jupiter
The inner planets are mostly made of iron and rock.
I believe the planet with low air pressure and that is mostly made of CO2 is Mars.
Earth is the planet that fits this description. It contains approximately 70% water on its surface and its atmosphere is primarily composed of nitrogen, with oxygen being the second most abundant gas.
Earth. Over 70% of Earth's surface is covered by water.
Pluto is a solid planet. Pluto is made mostly of ice, although the core is most likely rock with metal in it.