Select T/F for each of the following statements regarding Platinum Group Metals (PGMs): Platinum group metals that were exposed to air are extremely corrosion resistant and unreactive because of the very strong and coherent oxide layer that forms on their surfaces. The lower members of the platinum group metals, especially, are extremely dense because their crystal structures are close-packed and these atoms tend to offer numerous d electrons in a metallic bond, resulting in highly efficient packing of relatively heavy metal ions in the bulk metal. The extremely high bond strengths of the PGMs result in very low thermal expansion coefficients and extremely high elastic moduli. Because PGMs tend to donate so many electrons to the bulk metal when forming metallic bonds (up to 8 donated electrons), these metals feature a high concentration of "free" electrons that result in extremely high electrical conductivities compared to metals that feature a more typical valence state (1-2 donated electrons). PGM's are extremely rare in the earth's crust, resulting in extremely high prices and limited-quantity use for specialty applications.