Basically, the Solar System is made up of the Sun and the nine planets with asteroids and satellites. The nine planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto, in that order from the Sun. However, in 2006, Astronomers ruled that Pluto should no longer be considered a planet. So, we can say that the Solar System is made up of the Sun and eight planets, from Mercury to Neptune.
Ordinarily, Mercury should be the hottest planet in the Solar System considering the fact that it is the closest planet to the Sun. Alas! Mercury is not. Rather, Venus is the hottest planet in the Solar System! But why?
Venus is the hottest planet in the Solar System because of its greenhouse effect. It traps heat from the Sun by virtue of its atmosphere. Its atmosphere is made up of mainly carbon(IV)oxide which is a greenhouse gas.
(Photo Credits: earthspacecircle.blogspot.com)