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.
A neutral phosphorus atom has 15 electrons. Two electrons can go into the 1 s subshell, 2 can go into the 2 s subshell, and 6 can go into the 2 p subshell. That leaves 5 electrons. Of those 5 electrons, 2 can go into the 3 s subshell, and the remaining 3 electrons can go into the 3 p subshell.