Answer:
Planets are formed of rock, dust and gasses. A planet has different layers. Terrestrial planets are made of rocks and dust and gases form its atmosphere. Jovian planets are composed of gases which may or may not have solid core.
In solar system, the first four planets are terrestrial and next four are Jovian.
Mercury has no atmosphere.
Venus has a very thick atmosphere composed of carbon-dioxide.
Earth's atmosphere is made up of Nitrogen and oxygen.
Mars has a very thin atmosphere composed of Carbon-dioxide.
The Jovian planets: Jupiter, Saturn, Uranus and Neptune are composed of Hydrogen. Neptune and Uranus are blue in color due to presence of Methane in their atmosphere.