In a $p-n$ junction diode not connected to any circuit

• A

  the potential is the same everywhere
• B

  the p-type side has a higher potential than the n-type side
• Correct answer
  C

  there is an electric field at the junction directed from the n-type side to p-type side
• D

  there is an electric field at the junction directed from the p-type side to n-type side

Solution

At junction a potential barrier/depletion layer is formed with $n$-side at higher potential and p-side at lower potential. Therefore, there is an electric field at the junction directed from the n-side to p-side.

Hence, the correct answer is option: 'C'.