18. Which of the following statements is false? (A) an orbital can accommodate at most two electrons (B) the electron density at a point is proportional to at that point (C) the spin quantum number of an electron must be either +1/2 or -1/2 (D) a 2p orbital is more penetrating than a 2s； that is, it has a higher clectron density near the nucleus and inside the charge cloud of a Is orbital (E) in the usual order of filling, the 6s orbital is filled before the 4f orbital