well probably because when the solar system formed, the sunwas made of gas and dust, the remaining gas and dust not used on the sun became the planets, most likely during the formation of the planets...
it would be Pluto but its a dwaf planet
Yes, it is actually the smallest gas giant.
Neptune is a gas giant. The outer four planets, Jupiter, Saturn, Uranus, and Neptune are all gas giants.
It is a gas giant.