Answer:
electrons fill lower energy levels first before occupying higher energy levels.
Explanation:
The Aufbau's principle describes that electrons fill lower energy levels first before occupying higher energy levels.
In writing the electronic configuration of atoms, the Aufbau's principle is one of the most important principles to consider.
It states that "sublevels with with lower energies are filled up before those with higher energies".
Sublevels do not fill up in numerical order.
