Wikipedia Zener Diode
Circuit VI, 1. What is the voltage across the zener diode? (it's reverse breakdown is about ??? (Look at data sheet)
Circuit VII, 2. With R = 1 kohm, what is the current through the LED? From data sheet, it's forward threshold voltage is about 2.3 V
Physical understanding, Wikipedia article, Heavy doping, Thin depletion region, Thinner region, higher / lower e-field?
Practical understanding, I-V curves