I believe it is useful as it shows how electrons are distributed in the shells (energy levels) of an iron atom. An atom is the smallest particle of an element that can take part in a chemical reaction. It contains the nucleus and the shells (energy levels). the nucleus contains protons and neutrons while the shells contain electrons.
I belive it's the black chair because they were asking which chair experienced the most force in the begining and the black chair had the most force given.
