What is the value of the current $I$ flowing through the Zener diode in the given circuit? (in $mA$)

Explain the use of a Zener diode as a voltage regulator by drawing a circuit diagram.

$A$ $9\,V$ stabilized voltage supply is required to run a car stereo system from the car's $12\,V$ battery. $A$ Zener diode with $V_z = 9\,V$ and $P_{max} = 0.27\,W$ is to be used as the voltage regulator. The load resistance is $450\,\Omega$. The value of the series resistor $R_s$ is....$\Omega$.

$A$ Zener diode having breakdown voltage $V_z = 6 \, V$ is used in a voltage regulator circuit as shown in the figure. The minimum current required to pass through the Zener to act as a voltage regulator is $10 \, mA$ and the maximum allowed current through the Zener is $40 \, mA$. The maximum value of $R_s$ for the Zener to act as a voltage regulator is (in $\Omega$)

The incorrect statement about the property of a Zener diode is

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