A Zener diode when used as a voltage regulator, is connected
(a) in forward bias.
(b) in reverse bias.
(c) in parallel to the load.
(d) in series to the load.

A. (a) and (b) are correct
B. (b) and (c) are correct
C. Only (a) is correct
D. Only (d) is correct

Hint: A Semiconductor Diode blocks current in the reverse direction, but will suffer from premature breakdown or damage if the reverse voltage applied across becomes too high.

Complete step by step solution:
When Zener diode is biased in the forward direction it behaves like a normal signal diode passing the current increasing linearly with voltage, but as soon as a reverse voltage applied across the Zener diode attains the breakdown voltage of the device, a large current starts to flow through the diode. Thus, for a constant voltage large current will flow through it. Hence, it always connected in parallel to the load.

Hence option B is correct answer.

Additional Information:
Zener Diodes are widely used as Shunt Voltage Regulators to regulate the voltage across small loads. Zener Diodes have a sharp reverse breakdown voltage and breakdown voltage will be constant for a wide range of currents. Thus we will connect the zener diode parallel to the load such that the applied voltage will reverse bias it. Thus if the reverse bias voltage across the zener diode exceeds the knee voltage, the voltage across the load will be constant.

Note: The reverse bias voltage across the zener diode exceeds the knee voltage, the voltage across the load will be constant.