The Allegory of the Cave. The dialogue between Socrates and Glaucon is probably fictitious and composed by Plato; whether or not the allegory originated with Socrates, or if Plato is using his mentor as a stand-in for his own idea, is unclear. In the dialogue, Socrates asks Glaucon to imagine a cave, in which prisoners are kept.
The d sublevel consists of five orbitals that can hold a maximum of  two electrons each. The total maximum number of electrons that the  d sublevel can hold is 10 electrons.
In writing the electron configuration for sodium the first two electrons will go in the 1s orbital. Since 1s can only hold two electrons the next 2 electrons for sodium go in the 2s orbital. The nex six electrons will go in the 2p orbital. The p orbital can hold up to six electrons.