In the circuit shown below, minimum zener diode current will be ___mA

For minimum Zener diode current, the current in series resistance should also be minimum.

Thus, for that we have to take lower range of battery potential. i.e 100V.

Potential across Zener diode = 60V

Potential across series resistance = 100-60=40V

$\begin{array}{l}{\mathrm{I}}_{\mathrm{L}}=\frac{60}{10\times {10}^3}=6\mathrm{mA}\\ \mathrm{I}=\frac{40}{4\times {10}^3}=10\mathrm{mA}\\ {\mathrm{I}}_{\mathrm{Z}}=\mathrm{I}-{\mathrm{I}}_{\mathrm{L}}=4\mathrm{mA}\end{array}$