B. According to the information obtained from a cell in the periodic table, the atomic number of the element is 34, and atomic number = proton number, so the proton number of the element selenium is 34, so the statement is correct.
C, when the number of protons = the number of electrons outside the nucleus, for the atom, by the atomic structure of selenium schematic, then 34 = 2 + 8 + x + 6, the solution x = 18, so the option statement is correct.
D, by the atomic structure of selenium schematic diagram, the number of electrons in the outermost layer of the atom is 6, in the chemical reaction, selenium atoms are easy to get 2 electrons to form a stable structure, so the option statement is wrong.
The choice of D.