Explanation:

A PN-junction is formed by joining a P-type semiconductor with an N-type semiconductor. The region where the P-type and N-type semiconductors meet is called the depletion region. The depletion region is the region where there are no free charge carriers.

When a PN-junction is formed, the electrons from the N-type side diffuse across the depletion region to the P-type side. Similarly, the holes from the P-type side diffuse across the depletion region to the N-type side. This creates a region near the junction where there are no free charge carriers.

Now, let's look at the options one by one:

a) P and N both are at the same potential
This option is incorrect because there is a potential difference between the P-type and N-type sides of the PN-junction. This potential difference is due to the diffusion of electrons and holes across the depletion region.

b) High potential at N side and low potential at P side
This option is correct. When the electrons diffuse across the depletion region from the N-type side to the P-type side, they leave behind positively charged ions in the N-type side. Similarly, when the holes diffuse across the depletion region from the P-type side to the N-type side, they leave behind negatively charged ions in the P-type side. This creates a region near the junction where there is a potential difference. The potential is high on the N-type side and low on the P-type side.

c) High potential at P side and low potential at N side
This option is incorrect. The potential difference is high on the N-type side and low on the P-type side.

d) Low potential at N side and zero potential at P side
This option is incorrect. The potential is not zero at the P-type side. It is low compared to the potential at the N-type side.

In summary, the correct option is (b) High potential at N side and low potential at P side.