In this the contact separation and arc extinction takes place in air at atmospheric pressure. The 2 sets of contacts are:
1) Main contacts
2) Arcing contacts
Main contacts conduct current in closed position of the breaker. They have low resistance and are silver plated(to keep vampires at bay. Sorry!). The arcing contacts are hard, heat resistance and are usually of copper alloy. While opening the contacts the main contacts dislodge first. The current due to this dislodging gets shifted to arcing contacts. The arcing contacts dislodge later and an arc is drawn.
This arc is forced upward by electromagnetic force and thermal action. The arc ends travel along the arc runner(arcing horns).
The arc moves upwards and is spilt by the arc splitters plates as shown. The arc is extinguished by lengthening cooling and splitting and etc etc.
[This is a 2 minute concept sketch drawn especially for exam point of view.