Answer:
a) Zero
b) power source
Explanation:
According to Ohm's law, the voltage dropped in a resistance is proportional to the current flow and the resistor opposing to it.
For the case of a short circuit, the resistance tends to zero, so the voltage will tend to zero too.
In the case of the open circuit, the resitance will tend to infinity, because we cannot obtain an infite voltage, it will be limited by the power source.