Read the following statements with reference to electronic devices.

(A) A transistor is used as a rectifier

(B) A zener diode is used as a voltage regulator 

(C) A NOT gate is a universal gate

(D) A transistor is used as an amplifier

(E) A photodiode is used as an oscillator

Choose the correct answer from the options given below:

Concept:

A transistor:

• A transistor can be used as a switch or as an amplifier, but not as a rectifier.
• A rectifier is a device that converts alternating current (AC) to direct current (DC) by allowing current to flow in only one direction.
• A transistor can be used as an amplifier, amplifying a small signal into a larger one, or as a switch, allowing or blocking the flow of current.

Zener diode:

• A Zener diode is a type of diode that is designed to operate in the reverse breakdown region of its voltage-current characteristic curve.
• This makes it useful as a voltage regulator, maintaining a constant voltage across a load even as the input voltage varies.

NOT Gate:

• A NOT gate is not a universal gate, as it cannot be used to implement all possible Boolean functions. In contrast, NAND and NOR gates are universal gates, as they can be used to implement any Boolean function.

A photodiode:

• A photodiode is a type of semiconductor device that converts light into electrical current.
• It is not typically used as an oscillator, which is a device that generates a repetitive signal without the need for an external input signal.

From the above, it is clear that statements (B) and (D) are correct.

So, the correct answer is option (2).