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.
Oxygen's ground state electron configuration is #1s^(2)2s^(2)2p^(4)#. Oxygen has atomic number 8, so it has 8 electrons. Each s subshell can only hold 2 electrons before it begins to fill a p subshell.