A superconductor is a material that loses all electrical resistance below a characteristic temperature called the superconducting transitiontemperature. Which graph represents the behavior of a superconductor? (LO 12.13)(a)
(b)
(c)
(d)

The following diagrams represent the electron population ofmolecular orbitals for different substances. What diagram correspondsto magnesium oxide, germanium, and tin? (LO 12.8)

(a) Diagram 1 = tin, diagram 2 = magnesium oxide,diagram 3 = germanium(b) Diagram 1 = germanium, diagram 2 = magnesiumoxide, diagram 3 = tin(c) Diagram 1 = germanium, diagram 2 = tin, diagram3 = magnesium oxide(d) Diagram 1 = magnesium oxide, diagram 2 = tin,diagram 3 = germanium

The molecular orbital diagram of a doped semiconductor is shown below. If the semiconductor is silicon, does the diagram represent n-type or p-type doping and which of the following elements could be dopant? (LO 12.9)

(a) n-type, As (b) n-type, Ga (c) p-type, As (d) p-type, Ga

If the band-gap energy of a gallium phosphide (GaP) semiconductor is 222 kJ/mol, calculate the wavelength of light emitted in a GaP light-emitting diode (LED). (LO 12.11) (a) 186 nm (b) 245 nm (c) 539 nm (d) 854 nm

The following compound undergoes a phase transition from the solid to the smectic liquid crystal phase at 121 °C. Upon further heating, the compound undergoes another transition to liquid phase at 131 °C.

(b) Which image represents the arrangement of molecules at 135 °C?