Which of the following is heavily doped?

In a Zener regulated power supply, a Zener diode with $V_z = 6 \, V$ is used for regulation. The load current is $4 \, mA$ and the unregulated input voltage is $10 \, V$. To get a Zener current five times the load current, the value of the series resistor $R_S$ is nearly:

$A$ Zener diode with voltage $V_z = 6 \ V$ is used to maintain a constant voltage across a load resistance $R_L = 1000 \ \Omega$. $A$ series resistor $R_s = 100 \ \Omega$ is used. If the source $e.m.f$ is $E = 9 \ V$,then the power dissipated in the Zener diode is .......... $W$.

In the circuit shown, what will be the current through the $6 V$ zener diode?

In the circuit diagram shown in the figure,the current through the zener diode is (in $mA$)

The $I-V$ characteristics of an electronic device are shown in the figure. The device is $:-$