$A$ reverse biased Zener diode when operated in the breakdown region works as

Take the breakdown voltage of the zener diode used in the given circuit as $6\, V$. For the input voltage shown in the figure below, the time variation of the output voltage is: (Graphs drawn are schematic and not to scale)

$A$ diode has Zener voltage of $10 \text{ V}$ and maximum power dissipation of $0.5 \text{ W}$. The minimum resistance to be used in series with this diode for safety when it is connected to a $25 \text{ V}$ power supply is . . . . . . $\Omega$.

Which of the following is heavily doped?

$A$ Zener diode with a power rating of $1 \, W$ is to be used as a voltage regulator. If the Zener diode has a breakdown voltage of $5 \, V$ and it has to regulate an input voltage that fluctuates between $3 \, V$ and $7 \, V$,what should be the value of the series resistance $R_s$ for safe operation? (See figure)

Mention the use of a Zener diode.