Density. The gas giants all retained a good bit of hydrogen.
One key difference is their composition: terrestrial planets are mainly made of rock and metal, while gas giants are mostly composed of hydrogen and helium. Gas giants are also much larger in size and have thick atmospheres, while terrestrial planets have solid surfaces. Additionally, gas giants are typically located farther from the Sun in the outer regions of a solar system.
Its one of the gas giants, though some may argue that it is an `ice giant`.
Venus is one of the four rocky or terrestrial planets - not a gas giant.
Neptune is a gas giant planet in our solar system, primarily composed of hydrogen and helium with some ices and rocky material. It is one of the four gas giants along with Jupiter, Saturn, and Uranus.
There are the inner, terrestrial planets, also know as the rocky planets. Earth is one of these. Then there are the outer planets, also know as the gas planets or gas giants.
The question is not well-defined enough to answer. One common division is between "terrestrial" (rocky) planets and "jovian" (gas giant) planets. Some people make a distinction between "gas giants" (Jupiter and Neptune) and "ice giants" (Uranus and Neptune).
"Terrestrial planet" essentially means that the planet in question is a rocky, earthen planet where one could (in a space suit) step onto its defined surface. ("Jovian planets" refers to the gas planet of Jupiter and all the other gas giants in the solar system.)
A terrestrial planet is one with solid ground so the Gas Giants (Jupiter, Saturn, Uranus and Neptune) would not classify, as they have no solid surface.
Gas giants have the most moons compared to terrestrial planets. For example, Jupiter has the most known moons in our solar system with over 79, while Saturn follows closely behind with over 80 confirmed moons. Terrestrial planets like Earth have fewer moons, with only one natural satellite.
Mercury, Venus, Earth and Mars are all rock planets. The more technical term is terrestrial planets and they are composed of almost entirely of rock and metal. Each has a tiny amount of atmospheric gas and Earth has a tiny amount of liquid water. The other four planets are the gas giant planets, Jupiter, Saturn, Uranus and Neptune. That means they do not have a solid surface that is visible and much of the mass of the planet is the gaseous material. (All must have some small inner region consisting of rocky material, even if it is a tiny fraction of the mass that has been collected from stray asteroids.) The two gas giants closest to the Sun, Jupiter and Saturn, are the two largest in the solar system with Jupiter the largest of all. Both are composed mainly of hydrogen and helium. The outermost gas giants are called ice giants. Being colder, Uranus and Neptune have formed with substantial quantities of water, ammonium and methane with smaller amounts of hydrogen and helium in the outer regions. The water, ammonium and methane are solid at these temperatures, so the center of these planets is primarily frozen gasses with hydrogen and helium being predominant as an atmosphere.
The inner planets are called rocky or terrestrial, including Mercury, Venus, Earth, and Mars. That would make Neptune the odd one out - commonly referred to as an ice giant or gas giant.
The planet Saturn is one of many gas giants in our solar system.