The correct answer is: C. 0.7 V
The barrier potential is the voltage that exists across the depletion layer of a semiconductor diode. It is caused by the difference in the concentration of charge carriers on either side of the junction. The barrier potential is typically in the range of 0.5 to 0.7 volts, and it is an important factor in determining the current that flows through the diode.
Option A is incorrect because the barrier potential is not equal to zero.
Option B is incorrect because the barrier potential is not equal to 0.8 volts.
Option C is correct because the barrier potential is typically in the range of 0.5 to 0.7 volts.
Option D is incorrect because the barrier potential is not equal to 20 volts.
Option E is incorrect because the barrier potential is not equal to none of the above.