18. Which of the following statements is true? (A) We can determine the exact location of an electron if we know its energy. (B) An electron in a 2s orbital can have the same n, l, and ml quantum numbers as an electron in a 3s orbital. (C) Only three quantum numbers are needed to uniquely describe an electron. (D) In the building up of atoms, electrons occupy the 4f orbitals before the 6s orbitals. (E) Ni has 2 unpaired electrons in its 3d orbitals.