Which of the Following Statements Is Incorrect

Which of the following statements is incorrect?

A) Stern and Gerlach discovered electron spin by passing silver atoms through a magnetic field.
B) Hund's rule states that electrons are placed in the orbitals of a subshell in such a way as to give a maximum number of unpaired electrons.
C) The Pauli exclusion principle states that each electron in an atom must have its own unique set of quantum numbers.
D) Valence electrons consist of those electrons not contained within a noble-gas core or a pseudo-noble-gas core.
E) The building-up principle states that electrons are added to atoms in order of increasing principal quantum number.