Consider the following statements (A) and (B) and identify the correct answer.

(A) A zener diode is connected in reverse bias, when used as a voltage regulator

(B) The potential barrier of p-n junction lies between 0.1 V to 0.3 V.

The correct option is (A) is correct and (B) is incorrect.

Let us evaluate each statement individually to understand the underlying physics:

Statement (A): A zener diode is connected in reverse bias, when used as a voltage regulator
A Zener diode is a specially designed, heavily doped p-n junction diode. Unlike standard diodes, it is meant to operate safely in the reverse breakdown region (known as the Zener breakdown region).
When the reverse bias voltage across the Zener diode exceeds its breakdown voltage, the voltage across it remains constant even if there are large variations in the current. This unique characteristic allows it to maintain a stable output voltage across a load connected in parallel with it. Therefore, to function as a voltage regulator, a Zener diode must always be connected in reverse bias.
Thus, Statement (A) is correct.

Statement (B): The potential barrier of p-n junction lies between 0.1 V to 0.3 V.
The potential barrier (or barrier potential) of a p-n junction depends on the semiconductor material used:
1. For Germanium (Ge) diodes, the barrier potential is approximately 0.3 V.
2. For Silicon (Si) diodes, which are much more commonly used in modern electronics, the barrier potential is approximately 0.7 V.
Since the barrier potential of silicon diodes (0.7 V) lies outside the range of 0.1 V to 0.3 V, the general statement that the potential barrier of a p-n junction lies between 0.1 V to 0.3 V is incorrect.
Thus, Statement (B) is incorrect.

Conclusion:
Statement (A) is correct, and Statement (B) is incorrect.